51) main( )
{ void *vp; char ch = ‘g’, *cp = “goofy”; int j = 20; vp = &ch; printf(“%c”, *(char *)vp); vp = &j; printf(“%d”,*(int *)vp); vp = cp; printf(“%s”,(char *)vp + 3);
}
Answer:
g20fy
Since a void pointer is used it can be type casted to any other type pointer. vp = &ch stores address of char ch and the next statement prints the value stored in vp after type casting it to the proper data type pointer. the output is ‘g’. Similarly the output from second printf is ‘20’. The third printf statement type casts it to print the string from the 4th value hence the output is ‘fy’.
52) main ( )
{ static char *s[ ] = {“black”, “white”, “yellow”, “violet”}; char **ptr[ ] = {s+3, s+2, s+1, s}, ***p; p = ptr; **++p; printf(“%s”,*--*++p + 3);
}
Answer:
ck
Explanation:
In this problem we have an array of char pointers pointing to start of 4 strings. Then we have ptr which is a pointer to a pointer of type char and a variable p which is a pointer to a pointer to a pointer of type char. p hold the initial value of ptr, i.e. p = s+3. The next statement increment value in p by 1 , thus now value of p = s+2. In the printf statement the expression is evaluated *++p causes gets value s+1 then the pre decrement is executed and we get s+1 – 1 = s . the indirection operator now gets the value from the array of s and adds 3 to the starting address. The string is printed starting from this position. Thus, the output is ‘ck’.
53) main()
{ int i, n; char *x = “girl”; n = strlen(x); *x = x[n]; for(i=0; i<n; ++i)
{ printf(“%s\n”,x); x++;
} }
Answer:
(blank space) irl rl l
Explanation:
Here a string (a pointer to char) is initialized with a value “girl”. The strlen function returns the length of the string, thus n has a value 4. The next statement assigns value at the nth location (‘\0’) to the first location. Now the string becomes “\0irl” . Now the printf statement prints the string after each iteration it increments it starting position. Loop starts from 0 to
4. The first time x[0] = ‘\0’ hence it prints nothing and pointer value is incremented. The second time it prints from x[1] i.e “irl” and the third time it prints “rl” and the last time it prints “l” and the loop terminates.
54) int i,j; for(i=0;i<=10;i++) { j+=5; assert(i<5); }
Answer:
Runtime error: Abnormal program termination. assert failed (i<5), <file name>,<line number>
Explanation:
asserts are used during debugging to make sure that certain conditions are satisfied. If assertion fails, the program will terminate reporting the same. After debugging use,
#undef NDEBUG and this will disable all the assertions from the source code. Assertion is a good debugging tool to make use of.
55) main() { int i=-1; +i; printf("i = %d, +i = %d \n",i,+i); }
Answer:
i = -1, +i = -1
Explanation:
Unary + is the only dummy operator in C. Where-ever it comes you can just ignore it just because it has no effect in the expressions (hence the name dummy operator).
56) What are the files which are automatically opened when a C file is executed?
Answer:
stdin, stdout, stderr (standard input,standard output,standard error).
57) what will be the position of the file marker?
a: fseek(ptr,0,SEEK_SET);
b: fseek(ptr,0,SEEK_CUR);
Answer :
a: The SEEK_SET sets the file position marker to the starting of the file.
b: The SEEK_CUR sets the file position marker to the current position of the file.
58) main() { char name[10],s[12]; scanf(" \"%[^\"]\"",s); } How scanf will execute?
Answer:
First it checks for the leading white space and discards it.Then it matches with a quotation mark and then it reads all character upto another quotation mark.
59) What is the problem with the following code segment? while ((fgets(receiving array,50,file_ptr)) != EOF) ;
Answer & Explanation:
fgets returns a pointer. So the correct end of file check is checking for != NULL.
60) main()
{ main(); }
Answer:
Runtime error : Stack overflow.
Explanation:
main function calls itself again and again. Each time the function is called its return address is stored in the call stack. Since there is no condition to terminate the function call, the call stack overflows at runtime. So it terminates the program and results in an error.
61) main() { char *cptr,c; void *vptr,v; c=10; v=0; cptr=&c; vptr=&v; printf("%c%v",c,v); }
Answer:
Compiler error (at line number 4): size of v is Unknown.
Explanation:
You can create a variable of type void * but not of type void, since void is an empty type. In the second line you are creating variable vptr of type void * and v of type void hence an error.
62) main() { char *str1="abcd"; char str2[]="abcd"; printf("%d %d %d",sizeof(str1),sizeof(str2),sizeof("abcd")); }
Answer:
2 5 5
Explanation:
In first sizeof, str1 is a character pointer so it gives you the size of the pointer variable. In second sizeof the name str2 indicates the name of the array whose size is 5 (including the '\0' termination character). The third sizeof is similar to the second one.
63) main() { char not; not=!2; printf("%d",not); }
Answer:
0
Explanation:
! is a logical operator. In C the value 0 is considered to be the boolean value FALSE, and any non-zero value is considered to be the boolean value TRUE. Here 2 is a non-zero value so TRUE. !TRUE is FALSE (0) so it prints 0.
64) #define FALSE -1 #define TRUE 1 #define NULL 0 main() {
if(NULL) puts("NULL"); else if(FALSE) puts("TRUE"); else puts("FALSE"); }
Answer:
TRUE
Explanation: The input program to the compiler after processing by the preprocessor is, main(){ if(0)
puts("NULL"); else if(-1) puts("TRUE"); else
puts("FALSE"); } Preprocessor doesn't replace the values given inside the double quotes. The check by if condition is boolean value false so it goes to else. In second if -1 is boolean value true hence "TRUE" is printed.
65) main() { int k=1; printf("%d==1 is ""%s",k,k==1?"TRUE":"FALSE"); }
Answer:
1==1 is TRUE
Explanation:
When two strings are placed together (or separated by white-space) they are concatenated (this is called as "stringization" operation). So the string is as if it is given as "%d==1 is %s". The conditional operator( ?: ) evaluates to "TRUE".
66) main() { int y; scanf("%d",&y); // input given is 2000 if( (y%4==0 && y%100 != 0) || y%100 == 0 )
printf("%d is a leap year"); else printf("%d is not a leap year"); }
Answer:
2000 is a leap year
Explanation:
An ordinary program to check if leap year or not.
67) #define max 5 #define int arr1[max] main() { typedef char arr2[max]; arr1 list={0,1,2,3,4}; arr2 name="name"; printf("%d %s",list[0],name); }
Answer:
Compiler error (in the line arr1 list = {0,1,2,3,4})
Explanation:
arr2 is declared of type array of size 5 of characters. So it can be used to declare the variable name of the type arr2. But it is not the case of arr1. Hence an error.
Rule of Thumb:
#defines are used for textual replacement whereas typedefs are used for declaring new types.
68) int i=10; main() {
extern int i; { int i=20;
{ const volatile unsigned i=30; printf("%d",i);
} printf("%d",i);
} printf("%d",i); }
Answer:
30,20,10
Explanation:
'{' introduces new block and thus new scope. In the innermost block i is declared as,
const volatile unsigned which is a valid declaration. i is assumed of type int. So printf prints 30. In the next block, i has value 20 and so printf prints 20. In the outermost block, i is declared as extern, so no storage space is allocated for it. After compilation is over the linker resolves it to global variable i (since it is the only variable visible there). So it prints i's value as 10.
69) main()
{ int *j; {
int i=10; j=&i; } printf("%d",*j);
}
Answer:
10
Explanation: The variable i is a block level variable and the visibility is inside that block only. But the lifetime of i is lifetime of the function so it lives upto the exit of main function. Since the i is still allocated space, *j prints the value stored in i since j points i.
70) main() { int i=-1; -i; printf("i = %d, -i = %d \n",i,-i); }
Answer:
i = -1, -i = 1
Explanation:
-i is executed and this execution doesn't affect the value of i. In printf first you just print the value of i. After that the value of the expression -i = -(-1) is printed.
71) #include<stdio.h> main()
{ const int i=4; float j; j = ++i; printf("%d %f", i,++j);
} Answer: Compiler error Explanation: i is a constant. you cannot change the value of constant
72) #include<stdio.h> main() {
int a[2][2][2] = { {10,2,3,4}, {5,6,7,8} }; int *p,*q; p=&a[2][2][2]; *q=***a; printf("%d..%d",*p,*q);
}
Answer:
garbagevalue..1
Explanation:
p=&a[2][2][2] you declare only two 2D arrays. but you are trying to access the third 2D(which you are not declared) it will print garbage values. *q=***a starting address of a is assigned integer pointer. now q is pointing to starting address of a.if you print *q meAnswer:it will print first element of 3D array.
73) #include<stdio.h> main()
{ register i=5; char j[]= "hello";
printf("%s %d",j,i); }
Answer:
hello 5
Explanation: if you declare i as register compiler will treat it as ordinary integer and it will take integer value. i value may be stored either in register or in memory.
74) main()
{ int i=5,j=6,z; printf("%d",i+++j);
}
Answer:
11
Explanation:
the expression i+++j is treated as (i++ + j)
76) struct aaa{ struct aaa *prev; int i; struct aaa *next; };
main()
{ struct aaa abc,def,ghi,jkl; int x=100; abc.i=0;abc.prev=&jkl; abc.next=&def; def.i=1;def.prev=&abc;def.next=&ghi; ghi.i=2;ghi.prev=&def; ghi.next=&jkl; jkl.i=3;jkl.prev=&ghi;jkl.next=&abc; x=abc.next->next->prev->next->i; printf("%d",x);
}
Answer:
2
Explanation:
above all statements form a double circular linked list; abc.next->next->prev->next->i this one points to "ghi" node the value of at particular node is 2.
77) struct point { int x; int y; };
struct point origin,*pp; main() { pp=&origin; printf("origin is(%d%d)\n",(*pp).x,(*pp).y); printf("origin is (%d%d)\n",pp->x,pp->y); }
Answer:
origin is(0,0) origin is(0,0)
Explanation: pp is a pointer to structure. we can access the elements of the structure either with arrow mark or with indirection operator.
Note:
Since structure point is globally declared x & y are initialized as zeroes
78) main()
{ int i=_l_abc(10); printf("%d\n",--i);
} int _l_abc(int i) {
return(i++); }
Answer:
9
Explanation:
return(i++) it will first return i and then increments. i.e. 10 will be returned.
79) main()
{ char *p; int *q; long *r; p=q=r=0; p++; q++; r++; printf("%p...%p...%p",p,q,r);
}
Answer:
0001...0002...0004
Explanation:
++ operator when applied to pointers increments address according to their corresponding data-types.
80) main()
{ char c=' ',x,convert(z); getc(c);
if((c>='a') && (c<='z')) x=convert(c); printf("%c",x);
} convert(z) {
return z-32; }
Answer:
Compiler error
Explanation:
declaration of convert and format of getc() are wrong.
81) main(int argc, char **argv) { printf("enter the character"); getchar(); sum(argv[1],argv[2]); } sum(num1,num2) int num1,num2; { return num1+num2; } Answer: Compiler error. Explanation: argv[1] & argv[2] are strings. They are passed to the function sum without converting it to integer values.
82) # include <stdio.h> int one_d[]={1,2,3}; main() { int *ptr; ptr=one_d; ptr+=3; printf("%d",*ptr); } Answer: garbage value Explanation: ptr pointer is pointing to out of the array range of one_d.
83) # include<stdio.h> aaa() {
printf("hi");
}
bbb(){ printf("hello"); }
ccc(){ printf("bye"); }
main()
{ int (*ptr[3])(); ptr[0]=aaa; ptr[1]=bbb; ptr[2]=ccc; ptr[2]();
} Answer: bye
Explanation:
ptr is array of pointers to functions of return type int.ptr[0] is assigned to address of the function aaa. Similarly ptr[1] and ptr[2] for bbb and ccc respectively. ptr[2]() is in effect of writing ccc(), since ptr[2] points to ccc.
85) #include<stdio.h> main() { FILE *ptr; char i; ptr=fopen("zzz.c","r"); while((i=fgetch(ptr))!=EOF) printf("%c",i); } Answer: contents of zzz.c followed by an infinite loop Explanation: The condition is checked against EOF, it should be checked against NULL.
86) main() { int i =0;j=0; if(i && j++) printf("%d..%d",i++,j); printf("%d..%d,i,j); } Answer:
0..0
Explanation:
The value of i is 0. Since this information is enough to determine the truth value of the boolean expression. So the statement following the if statement is not executed. The values of i and j remain unchanged and get printed.
87) main()
{ int i; i = abc(); printf("%d",i);
} abc() {
_AX = 1000; }
Answer:
1000
Explanation:
Normally the return value from the function is through the information from the accumulator. Here _AH is the pseudo global variable denoting the accumulator. Hence, the value of the accumulator is set 1000 so the function returns value 1000.
88) int i; main(){ int t; for ( t=4;scanf("%d",&i)-t;printf("%d\n",i))
printf("%d--",t--); } // If the inputs are 0,1,2,3 find the o/p
Answer:
4--0 3--1 2--2
Explanation:
Let us assume some x= scanf("%d",&i)-t the values during execution
will be, t i x 4 0 -4 3 1 -2 2 2 0
89) main(){ int a= 0;int b = 20;char x =1;char y =10;
if(a,b,x,y) printf("hello"); }
Answer:
hello
Explanation:
The comma operator has associativity from left to right. Only the rightmost value is returned and the other values are evaluated and ignored. Thus the value of last variable y is returned to check in if. Since it is a non zero value if becomes true so, "hello" will be printed.
90) main(){ unsigned int i; for(i=1;i>-2;i--) printf("c aptitude"); } Explanation: i is an unsigned integer. It is compared with a signed value. Since the both types doesn't match, signed is promoted to unsigned value. The unsigned equivalent of -2 is a huge value so condition becomes false and control comes out of the loop.
91) In the following pgm add a stmt in the function fun such that the address of 'a' gets stored in 'j'. main(){ int * j; void fun(int **); fun(&j); } void fun(int **k) { int a =0; /* add a stmt here*/ } Answer: *k = &a Explanation: The argument of the function is a pointer to a pointer.
92) What are the following notations of defining functions known as?
i. int abc(int a,float b) { /* some code */
}
ii. int abc(a,b)
int a; float b; {
/* some code*/ }
Answer:
i. ANSI C notation
ii. Kernighan & Ritche notation
93) main() { char *p; p="%d\n"; p++; p++; printf(p-2,300); }
Answer:
300
Explanation:
The pointer points to % since it is incremented twice and again decremented by 2, it points to '%d\n' and 300 is printed.
94) main(){ char a[100]; a[0]='a';a[1]]='b';a[2]='c';a[4]='d'; abc(a);
}
abc(char a[]){ a++; printf("%c",*a); a++; printf("%c",*a);
}
Explanation:
The base address is modified only in function and as a result a points to 'b' then after incrementing to 'c' so bc will be printed.
95) func(a,b) int a,b; {
return( a= (a==b) ); } main() { int process(),func(); printf("The value of process is %d !\n ",process(func,3,6)); } process(pf,val1,val2)
int (*pf) (); int val1,val2; { return((*pf) (val1,val2));
}
Answer:
The value if process is 0 !
Explanation:
The function 'process' has 3 parameters - 1, a pointer to another function 2 and 3, integers. When this function is invoked from main, the following substitutions for formal parameters take place: func for pf, 3 for val1 and 6 for val2. This function returns the result of the operation performed by the function 'func'. The function func has two integer parameters. The formal parameters are substituted as 3 for a and 6 for b. since 3 is not equal to 6, a==b returns 0. therefore the function returns 0 which in turn is returned by the function 'process'.
96) void main()
{ static int i=5; if(--i){
main(); printf("%d ",i); } }
Answer:
0 0 0 0
Explanation:
The variable "I" is declared as static, hence memory for I will be allocated for only once, as it encounters the statement. The function main() will be called recursively unless I becomes equal to 0, and since main() is recursively called, so the value of static I ie., 0 will be printed every time the control is returned.
97) void main()
{ int k=ret(sizeof(float)); printf("\n here value is %d",++k);
} int ret(int ret) {
ret += 2.5; return(ret); }
Answer:
Here value is 7
Explanation:
The int ret(int ret), ie., the function name and the argument name can be the same.
Firstly, the function ret() is called in which the sizeof(float) ie., 4 is passed, after the first expression the value in ret will be 6, as ret is integer hence the value stored in ret will have implicit type conversion from float to int. The ret is returned in main() it is printed after and preincrement.
98) void main()
{ char a[]="12345\0"; int i=strlen(a); printf("here in 3 %d\n",++i);
}
Answer:
here in 3 6
Explanation:
The char array 'a' will hold the initialized string, whose length will be counted from 0 till the null character. Hence the 'I' will hold the value equal to 5, after the pre-increment in the printf statement, the 6 will be printed.
99) void main()
{ unsigned giveit=-1; int gotit; printf("%u ",++giveit); printf("%u \n",gotit=--giveit);
}
Answer:
0 65535
Explanation:
100) void main()
{ int i; char a[]="\0"; if(printf("%s\n",a))
printf("Ok here \n"); else printf("Forget it\n"); }
Answer:
Ok here
Explanation:
Printf will return how many characters does it print. Hence printing a null character returns 1 which makes the if statement true, thus "Ok here" is printed.
101) void main()
{ void *v; int integer=2; int *i=&integer; v=i; printf("%d",(int*)*v);
}
Answer:
Compiler Error. We cannot apply indirection on type void*.
Explanation:
Void pointer is a generic pointer type. No pointer arithmetic can be done on it. Void pointers are normally used for,
1 Passing generic pointers to functions and returning such pointers.
2 As a intermediate pointer type.
3 Used when the exact pointer type will be known at a later point of time.
102) void main()
{ int i=i++,j=j++,k=k++; printf(“%d%d%d”,i,j,k);
}
Answer:
Garbage values.
Explanation:
An identifier is available to use in program code from the point of its declaration.
So expressions such as i = i++ are valid statements. The i, j and k are automatic variables and so they contain some garbage value. Garbage in is garbage out (GIGO).
103) void main()
{ static int i=i++, j=j++, k=k++; printf(“i = %d j = %d k = %d”, i, j, k);
}
Answer:
i = 1 j = 1 k = 1
Explanation:
Since static variables are initialized to zero by default.
104) void main() {
while(1){ if(printf("%d",printf("%d"))) break; else continue; } }
Answer:
Garbage values
Explanation:
The inner printf executes first to print some garbage value. The printf returns no of characters printed and this value also cannot be predicted. Still the outer printf prints something and so returns a non-zero value. So it encounters the break statement and comes out of the while statement.
104) main()
{ unsigned int i=10; while(i-->=0)
printf("%u ",i);
}
Answer:
10 9 8 7 6 5 4 3 2 1 0 65535 65534…..
Explanation:
Since i is an unsigned integer it can never become negative. So the expression i-- >=0 will always be true, leading to an infinite loop.
105) #include<conio.h> main() {
int x,y=2,z,a; if(x=y%2) z=2; a=2; printf("%d %d ",z,x);
}
Answer:
Garbage-value 0
Explanation:
The value of y%2 is 0. This value is assigned to x. The condition reduces to if (x) or in other words if(0) and so z goes uninitialized. Thumb Rule: Check all control paths to write bug free code.
106) main() { int a[10];
printf("%d",*a+1-*a+3); }
Answer:
4
Explanation:
*a and -*a cancels out. The result is as simple as 1 + 3 = 4 !
107) #define prod(a,b) a*b main() {
int x=3,y=4; printf("%d",prod(x+2,y-1)); }
Answer:
10
Explanation:
The macro expands and evaluates to as: x+2*y-1 => x+(2*y)-1 => 10
108) main()
{ unsigned int i=65000; while(i++!=0); printf("%d",i);
}
Answer:
1
Explanation:
Note the semicolon after the while statement. When the value of i becomes 0 it comes out of while loop. Due to post-increment on i the value of i while printing is 1.
109) main()
{ int i=0; while(+(+i--)!=0)
i-=i++; printf("%d",i); }
Answer:
-1
Explanation:
Unary + is the only dummy operator in C. So it has no effect on the expression and now the while loop is, while(i--!=0) which is false and so breaks out of while loop. The value –1 is printed due to the post-decrement operator.
113) main()
{ float f=5,g=10; enum{i=10,j=20,k=50}; printf("%d\n",++k); printf("%f\n",f<<2); printf("%lf\n",f%g); printf("%lf\n",fmod(f,g));
}
Answer:
Line no 5: Error: Lvalue required Line no 6: Cannot apply leftshift to float Line no 7: Cannot apply mod to float
Explanation:
Enumeration constants cannot be modified, so you cannot apply ++. Bit-wise operators and % operators cannot be applied on float values. fmod() is to find the modulus values for floats as % operator is for ints.
110) main()
{ int i=10; void pascal f(int,int,int); f(i++,i++,i++); printf(" %d",i);
} void pascal f(integer :i,integer:j,integer :k) {
write(i,j,k); }
Answer:
Compiler error: unknown type integer Compiler error: undeclared function write
Explanation:
Pascal keyword doesn’t mean that pascal code can be used. It means that the function follows Pascal argument passing mechanism in calling the functions.
111) void pascal f(int i,int j,int k) {
printf(“%d %d %d”,i, j, k); } void cdecl f(int i,int j,int k) {
printf(“%d %d %d”,i, j, k); } main()
{ int i=10; f(i++,i++,i++); printf(" %d\n",i); i=10; f(i++,i++,i++); printf(" %d",i);
}
Answer:
10 11 12 13 12 11 10 13
Explanation:
Pascal argument passing mechanism forces the arguments to be called from left to right. cdecl is the normal C argument passing mechanism where the arguments are passed from right to left.
112). What is the output of the program given below
main()
{ signed char i=0; for(;i>=0;i++) ; printf("%d\n",i);
}
Answer
-128
Explanation
Notice the semicolon at the end of the for loop. THe initial value of the i is set to 0. The inner loop executes to increment the value from 0 to 127 (the positive range of char) and then it rotates to the negative value of -128. The condition in the for loop fails and so comes out of the for loop. It prints the current value of i that is
128.
113) main()
{ unsigned char i=0; for(;i>=0;i++) ; printf("%d\n",i);
}
Answer
infinite loop
Explanation
The difference between the previous question and this one is that the char is declared to be unsigned. So the i++ can never yield negative value and i>=0 never becomes false so that it can come out of the for loop.
114) main()
{ char i=0; for(;i>=0;i++) ; printf("%d\n",i);
}
Answer:
Behavior is implementation dependent.
Explanation:
The detail if the char is signed/unsigned by default is implementation dependent. If the implementation treats the char to be signed by default the program will print –128 and terminate. On the other hand if it considers char to be unsigned by default, it goes to infinite loop.
Rule:
You can write programs that have implementation dependent behavior. But dont write programs that depend on such behavior.
115) Is the following statement a declaration/definition. Find what does it mean? int (*x)[10];
Answer
Definition. x is a pointer to array of(size 10) integers.
Apply clock-wise rule to find the meaning of this definition.
116). What is the output for the program given below
typedef enum errorType{warning, error, exception,}error; main() {
error g1; g1=1; printf("%d",g1);
}
Answer
Compiler error: Multiple declaration for error
Explanation
The name error is used in the two meanings. One means that it is a enumerator constant with value 1. The another use is that it is a type name (due to typedef) for enum errorType. Given a situation the compiler cannot distinguish the meaning of error to know in what sense the error is used:
error g1;
51
g1=error;
// which error it refers in each case?
When the compiler can distinguish between usages then it will not
issue error (in pure technical terms, names can only be overloaded in
different namespaces).
Note: the extra comma in the declaration,
enum errorType{warning, error, exception,}
is not an error. An extra comma is valid and is provided just for
programmer’s convenience.
117) typedef struct error{int warning, error, exception;}error;
main()
{
error g1;
g1.error =1;
printf("%d",g1.error);
}
Answer
1
Explanation
The three usages of name errors can be distinguishable by the compiler at any instance, so valid (they are in different namespaces). Typedef struct error{int warning, error, exception;}error;
This error can be used only by preceding the error by struct kayword as in:
struct error someError;
typedef struct error{int warning, error, exception;}error; This can be used only after . (dot) or -> (arrow) operator preceded by the variable name as in :
g1.error =1;
printf("%d",g1.error);
typedef struct error{int warning, error, exception;}error; This can be used to define variables without using the preceding struct keyword as in:
error g1; Since the compiler can perfectly distinguish between these three usages, it is perfectly legal and valid.
Note
This code is given here to just explain the concept behind. In real programming don’t use such overloading of names. It reduces the readability of the code. Possible doesn’t mean that we should use it!
118) #ifdef something int some=0; #endif
main()
{ int thing = 0; printf("%d %d\n", some ,thing);
}
Answer:
Compiler error : undefined symbol some
Explanation:
This is a very simple example for conditional compilation. The name something is not already known to the compiler making the declaration int some = 0; effectively removed from the source code.
119) #if something == 0 int some=0; #endif
main()
{ int thing = 0; printf("%d %d\n", some ,thing);
}
Answer
0 0
Explanation
This code is to show that preprocessor expressions are not the same as the ordinary expressions. If a name is not known the preprocessor treats it to be equal to zero.
120). What is the output for the following program
main() { int arr2D[3][3]; printf("%d\n", ((arr2D==* arr2D)&&(* arr2D == arr2D[0])) ); }
Answer
1
Explanation
This is due to the close relation between the arrays and pointers. N dimensional arrays are made up of (N-1) dimensional arrays.
arr2D is made up of a 3 single arrays that contains 3 integers each .
arr2D arr2D[1] arr2D[2]
arr2D[3] The name arr2D refers to the beginning of all the 3 arrays. *arr2D refers to the start of the first 1D array (of 3 integers) that is the same address as arr2D. So the expression (arr2D == *arr2D) is true (1). Similarly, *arr2D is nothing but *(arr2D + 0), adding a zero doesn’t change the value/meaning. Again arr2D[0] is the another way of telling *(arr2D + 0). So the expression (*(arr2D + 0) == arr2D[0]) is true (1). Since both parts of the expression evaluates to true the result is true(1) and the same is printed.
121) void main()
{ if(~0 == (unsigned int)-1) printf(“You can answer this if you know how values are represented in memory”);
} Answer
You can answer this if you know how values are represented in memory Explanation
~ (tilde operator or bit-wise negation operator) operates on 0 to produce all ones to fill the space for an integer. –1 is represented in unsigned value as all 1’s and so both are equal.
122) int swap(int *a,int *b) {
*a=*a+*b;*b=*a-*b;*a=*a-*b; } main() {
int x=10,y=20; swap(&x,&y); printf("x= %d y = %d\n",x,y);
} Answer x = 20 y = 10
Explanation This is one way of swapping two values. Simple checking will help understand this.
123) main() { char *p = “ayqm”; printf(“%c”,++*(p++)); } Answer:
b
124) main()
{ int i=5; printf("%d",++i++);
}
Answer:
Compiler error: Lvalue required in function main
Explanation:
++i yields an rvalue. For postfix ++ to operate an lvalue is required.
125) main()
{ char *p = “ayqm”; char c; c = ++*p++; printf(“%c”,c);
}
Answer:
b
Explanation:
There is no difference between the expression ++*(p++) and ++*p++. Parenthesis just works as a visual clue for the reader to see which expression is first evaluated.
126) int aaa() {printf(“Hi”);} int bbb(){printf(“hello”);} iny ccc(){printf(“bye”);}
main() { int ( * ptr[3]) (); ptr[0] = aaa;
ptr[1] = bbb; ptr[2] =ccc; ptr[2]();
}
Answer:
bye
Explanation: int (* ptr[3])() says that ptr is an array of pointers to functions that takes no arguments and returns the type int. By the assignment ptr[0] = aaa; it means that the first function pointer in the array is initialized with the address of the function aaa. Similarly, the other two array elements also get initialized with the addresses of the functions bbb and ccc. Since ptr[2] contains the address of the function ccc, the call to the function ptr[2]() is same as calling ccc(). So it results in printing "bye".
127) main() { int i=5; printf(“%d”,i=++i ==6); }
Answer:
1
Explanation:
The expression can be treated as i = (++i==6), because == is of higher precedence than = operator. In the inner expression, ++i is equal to 6 yielding true(1). Hence the result.
128) main() { char p[ ]="%d\n"; p[1] = 'c'; printf(p,65); } Answer: A Explanation: Due to the assignment p[1] = ‘c’ the string becomes, “%c\n”. Since this string becomes the format string for printf and ASCII value of 65 is ‘A’, the same gets printed.
129) void ( * abc( int, void ( *def) () ) ) ();
Answer::
abc is a ptr to a function which takes 2 parameters .(a). an integer variable.(b). a ptrto a funtion which returns void. the return type of the function is void.
Explanation:
Apply the clock-wise rule to find the result.
130) main() { while (strcmp(“some”,”some\0”)) printf(“Strings are not equal\n”); }
Answer:
No output
Explanation:
Ending the string constant with \0 explicitly makes no difference. So “some” and “some\0” are equivalent. So, strcmp returns 0 (false) hence breaking out of the while loop.
131) main()
{ char str1[] = {‘s’,’o’,’m’,’e’}; char str2[] = {‘s’,’o’,’m’,’e’,’\0’}; while (strcmp(str1,str2)) printf(“Strings are not equal\n”);
}
Answer:
“Strings are not equal” “Strings are not equal” ….
Explanation:
If a string constant is initialized explicitly with characters, ‘\0’ is not appended automatically to the string. Since str1 doesn’t have null termination, it treats whatever the values that are in the following positions as part of the string until it randomly reaches a ‘\0’. So str1 and str2 are not the same, hence the result.
132) main()
{ int i = 3; for (;i++=0;) printf(“%d”,i);
}
Answer:
Compiler Error: Lvalue required.
Explanation:
As we know that increment operators return rvalues and hence it cannot appear on the left hand side of an assignment operation.
133) void main()
{ int *mptr, *cptr; mptr = (int*)malloc(sizeof(int)); printf(“%d”,*mptr); int *cptr = (int*)calloc(sizeof(int),1); printf(“%d”,*cptr);
}
Answer:
garbage-value 0
Explanation:
The memory space allocated by malloc is uninitialized, whereas calloc returns the allocated memory space initialized to zeros.
134) void main()
{ static int i; while(i<=10) (i>2)?i++:i--; printf(“%d”, i);
}
Answer:
32767
Explanation:
Since i is static it is initialized to 0. Inside the while loop the conditional operator evaluates to false, executing i--. This continues till the integer value rotates to positive value (32767). The while condition becomes false and hence, comes out of the while loop, printing the i value.
135) main()
{ int i=10,j=20; j = i, j?(i,j)?i:j:j; printf("%d %d",i,j);
}
Answer:
10 10
Explanation:
The Ternary operator ( ? : ) is equivalent for if-then-else statement. So the question can be written as: if(i,j) {
if(i,j) j = i; else j = j; } else j = j;
136) 1. const char *a;
1. char* const a;
2. char const *a; -Differentiate the above declarations.
Answer:
1. 'const' applies to char * rather than 'a' ( pointer to a constant char ) *a='F' : illegal a="Hi" : legal
2. 'const' applies to 'a' rather than to the value of a (constant pointer to
char ) *a='F' : legal a="Hi" : illegal
3. Same as 1.
137) main()
{ int i=5,j=10; i=i&=j&&10; printf("%d %d",i,j);
}
Answer:
1 10
Explanation:
The expression can be written as i=(i&=(j&&10)); The inner expression (j&&10) evaluates to 1 because j==10. i is 5. i = 5&1 is 1. Hence the result.
138) main()
{ int i=4,j=7; j = j || i++ && printf("YOU CAN"); printf("%d %d", i, j);
}
Answer:
4 1
Explanation:
The boolean expression needs to be evaluated only till the truth value of the expression is not known. j is not equal to zero itself means that the expression’s truth value is 1. Because it is followed by || and true || (anything) => true where (anything) will not be evaluated. So the remaining expression is not evaluated and so the value of i remains the same. Similarly when && operator is involved in an expression, when any of the operands become false, the whole expression’s truth value becomes false and hence the remaining expression will not be evaluated.
false && (anything) => false where (anything) will not be evaluated.
139) main()
{ register int a=2; printf("Address of a = %d",&a); printf("Value of a = %d",a);
}
Answer:
Compier Error: '&' on register variable
Rule to Remember: & (address of ) operator cannot be applied on register variables.
140) main()
{ float i=1.5; switch(i) {
case 1: printf("1"); case 2: printf("2"); default : printf("0");
} }
Answer:
Compiler Error: switch expression not integral
Explanation:
Switch statements can be applied only to integral types.
141) main()
{ extern i; printf("%d\n",i); {
int i=20; printf("%d\n",i); } }
Answer:
Linker Error : Unresolved external symbol i
Explanation:
The identifier i is available in the inner block and so using extern has no use in resolving it.
142) main()
{ int a=2,*f1,*f2; f1=f2=&a; *f2+=*f2+=a+=2.5; printf("\n%d %d %d",a,*f1,*f2);
}
Answer:
16 16 16
Explanation:
f1 and f2 both refer to the same memory location a. So changes through f1 and f2 ultimately affects only the value of a.
143) main()
{ char *p="GOOD"; char a[ ]="GOOD"; printf("\n sizeof(p) = %d, sizeof(*p) = %d, strlen(p) = %d", sizeof(p), sizeof(*p), strlen(p)); printf("\n sizeof(a) = %d, strlen(a) = %d", sizeof(a), strlen(a));
}
Answer:
sizeof(p) = 2, sizeof(*p) = 1, strlen(p) = 4 sizeof(a) = 5, strlen(a) = 4
Explanation:
sizeof(p) => sizeof(char*) => 2 sizeof(*p) => sizeof(char) => 1 Similarly, sizeof(a) => size of the character array => 5
When sizeof operator is applied to an array it returns the sizeof the array
and it is not the same as the sizeof the pointer variable. Here the sizeof(a) where a is the character array and the size of the array is 5 because the space necessary for the terminating NULL character should also be taken into account.
144) #define DIM( array, type) sizeof(array)/sizeof(type) main()
{ int arr[10]; printf(“The dimension of the array is %d”, DIM(arr, int));
}
Answer:
10
Explanation:
The size of integer array of 10 elements is 10 * sizeof(int). The macro expands to sizeof(arr)/sizeof(int) => 10 * sizeof(int) / sizeof(int) => 10.
145) int DIM(int array[]) { return sizeof(array)/sizeof(int ); } main() {
int arr[10]; printf(“The dimension of the array is %d”, DIM(arr)); }
Answer:
1
Explanation:
Arrays cannot be passed to functions as arguments and only the pointers can be passed. So the argument is equivalent to int * array (this is one of the very few places where [] and * usage are equivalent). The return statement becomes, sizeof(int *)/ sizeof(int) that happens to be equal in this case.
146) main()
{ static int a[3][3]={1,2,3,4,5,6,7,8,9}; int i,j; static *p[]={a,a+1,a+2}; for(i=0;i<3;i++) {
for(j=0;j<3;j++) printf("%d\t%d\t%d\t%d\n",*(*(p+i)+j), *(*(j+p)+i),*(*(i+p)+j),*(*(p+j)+i));
} }
Answer:
1 1 1 1 2 4 2 4 3 7 3 7 4 2 4 2
5 5 5 5 6 8 6 8 7 3 7 3 8 6 8 6 9 9 9 9
Explanation:
*(*(p+i)+j) is equivalent to p[i][j].
147) main()
{ void swap(); int x=10,y=8; swap(&x,&y); printf("x=%d y=%d",x,y);
} void swap(int *a, int *b) {
*a ^= *b, *b ^= *a, *a ^= *b; }
Answer:
x=10 y=8
Explanation:
Using ^ like this is a way to swap two variables without using a temporary variable and that too in a single statement. Inside main(), void swap(); means that swap is a function that may take any number of arguments (not no arguments) and returns nothing. So this doesn’t issue a compiler error by the call swap(&x,&y); that has two arguments. This convention is historically due to pre-ANSI style (referred to as Kernighan and Ritchie style) style of function declaration. In that style, the swap function will be defined as follows,
void swap() int *a, int *b {
*a ^= *b, *b ^= *a, *a ^= *b;
} where the arguments follow the (). So naturally the declaration for swap will look like, void swap() which means the swap can take any number of arguments.
148) main()
{ int i = 257; int *iPtr = &i; printf("%d %d", *((char*)iPtr), *((char*)iPtr+1) );
}
Answer:
1 1
Explanation:
The integer value 257 is stored in the memory as, 00000001 00000001, so the individual bytes are taken by casting it to char * and get printed.
149) main()
{ int i = 258; int *iPtr = &i; printf("%d %d", *((char*)iPtr), *((char*)iPtr+1) );
}
Answer:
2 1
Explanation:
The integer value 257 can be represented in binary as, 00000001 00000001. Remember that the INTEL machines are ‘small-endian’ machines. Small-endian means that the lower order bytes are stored in the higher memory addresses and the higher order bytes are stored in lower addresses. The integer value 258 is stored in memory as: 00000001 00000010.
150) main()
{ int i=300; char *ptr = &i; *++ptr=2; printf("%d",i);
}
Answer:
556
Explanation:
The integer value 300 in binary notation is: 00000001 00101100. It is stored in memory (small-endian) as: 00101100 00000001. Result of the expression *++ptr = 2 makes the memory representation as: 00101100 00000010. So the integer corresponding to it is 00000010 00101100 =>
556.
No comments:
Post a Comment