GATE CS 2018 Set 1 — Question 39

MCQ+2 / -0.67EasyPointers & Pointer ArithmeticC ProgrammingProgramming & Data Structures

Programming & Data Structures → C Programming → Pointers & Pointer Arithmetic

Last updated 5 September 2026

Question

Consider the following C program: #include<stdio.h> void fun1(char *s1, char *s2){ char *tmp; tmp = s1; s1 = s2; s2 = tmp; } void fun2(char **s1, char **s2){ char *tmp; tmp = *s1; *s1 = *s2; *s2 = tmp; } int main(){ char *str1 = "Hi", *str2 = "Bye"; fun1(str1, str2); printf("%s %s ", str1, str2); fun2(&str1, &str2); printf("%s %s", str1, str2); return 0; } The output of the program above is

Correct answer (A) Hi Bye Bye Hi Solution Let's trace the execution of the program: 1. char *str1 = "Hi", *str2 = "Bye"; initializes two pointers to string literals. 2. fun1(str1, str2); is called. In C, arguments are passed by value. fun1 receives copies of the pointers str1 and str2 . Swapping these local copies s1 and s2 inside fun1 has no effect on the original pointers str1 and str2 in main . 3. printf("%s %s ", str1, str2); prints the original values: Hi Bye (note the trailing space). 4. fun2(&str1, &str2); is called. This passes the addresses of the pointers str1 and str2 (pass-by-reference using pointers to pointers). 5. Inside fun2, *s1 refers to str1 and *s2 refers to str2 . The code swaps the values stored at these addresses. Thus, str1 now points to "Bye" and str2 points to "Hi". 6. printf("%s %s", str1, str2); prints the updated values: Bye Hi . Combining the outputs: Hi Bye Bye Hi . The correct option is (A). Turn this into a strength. Explore AI-powered practice and doubt support with Success Tracker.

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Correct answer (A) Hi Bye Bye Hi Solution Let's trace the execution of the program: 1. char *str1 = "Hi", *str2 = "Bye"; initializes two pointers to string literals. 2. fun1(str1, str2); is called. In C, arguments are passed by value. fun1 receives copies of the pointers str1 and str2 . Swapping these local copies s1 and s2 inside fun1 has no effect on the original pointers str1 and str2 in main . 3. printf("%s %s ", str1, str2); prints the original values: Hi Bye (note the trailing space). 4. fun2(&str1, &str2); is called. This passes the addresses of the pointers str1 and str2 (pass-by-reference using pointers to pointers). 5. Inside fun2, *s1 refers to str1 and *s2 refers to str2 . The code swaps the values stored at these addresses. Thus, str1 now points to "Bye" and str2 points to "Hi". 6. printf("%s %s", str1, str2); prints the updated values: Bye Hi . Combining the outputs: Hi Bye Bye Hi . The correct option is (A).

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