GATE CSE 2024 | Set 2 | Question: 23

Question

​​​Consider the following $\mathrm{C}$ function definition.

int f X(char * a) {

char * b =  a;

while (*b)

b ++;

return b - a; }

Which of the following statements is/are TRUE?

• A. The function call $\text{f X("a b c d''}$) will always return a value
• B. Assuming a character array $c$ is declared as char $c[ ]=$ "abcd" in main ( ), the function call $f X$ (c) will always return a value
• C. The code of the function will not compile
• D. Assuming a character pointer $\mathrm{C}$ is declared as char ${ }^{*} \mathrm{C}=$ "abcd" in main (), the function call $\mathrm{fX}(\mathrm{c})$ will always return a value

Comments

And the return value would be 1 according to pointer arithmetic

Answer 1

Answer is A,B,D

We are modifying the local variable inside the function.

#include<stdio.h>

int fX(char *a) {

    char *b = a;

    while (*b)

        b++;

    return b - a;

}

int main(){

    

    int result_A = fX("abcd");

    printf("Option A: Result of fX(\"abcd\"): %d\n", result_A);

    

    char c[] = "abcd";

    int result_B = fX(c);

    printf("Option B: Result of fX(c): %d\n", result_B);

    char *ptr_c = "abcd";

    int result_D = fX(ptr_c);

    printf("Option D: Result of fX(ptr_c): %d\n", result_D);

    

}

Answer 2

A,B,D is the answer.

The return value is 4.

Answer 3

Pointer b contains the address passed to the pointer c. Now every pointer when incremented increases it's value by the number equal to the size of data type for which it's a pointer. Also we know that the last char is followed by a null char. 

So when the b is assigned with null ptr, it breaks out of loop and returns the value of b - a. 

Note : b - a is actually the absolute address difference divided by the byte size of the data type for which it's a pointer.

So A, B, D all will always return value as the pointer will always become null ptr at some point.