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C Aptitude Questions and Answers



Predict the output or error(s) for the following:
16.      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.

17.       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.

18.      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'.

19.       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.

20.       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.

21.       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.

22.       void main()
{
            unsigned giveit=-1;
            int gotit;
            printf("%u ",++giveit);
            printf("%u \n",gotit=--giveit);
}

Answer:
 0 65535

23.    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.

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