GATE CS 2015 Set 2 — Question 21

MCQ+1 / -0.33MediumFunctions & RecursionC ProgrammingProgramming & Data StructuresPointers & Pointer ArithmeticArrays & Strings in C

Programming & Data Structures → C Programming → Arrays & Strings in C

Last updated 5 September 2026

Question

Consider the following function written in the C programming language. void foo(char *a){ if ( *a && *a != ' '){ foo(a+1); putchar(*a); } } The output of the above function on input "ABCD EFGH" is

Correct answer(D) DCBASolutionThe function foo is a recursive function that processes a string character by character. 1.The base case for the recursion is when *a is either the null terminator \0 (evaluated as false in C) or a space character ' '.2.For the input "ABCD EFGH", the function calls itself recursively for 'A', then 'B', then 'C', then 'D'.3.When the pointer reaches the space character between 'D' and 'E', the condition *a != ' ' fails, and the recursion stops.4.Because putchar(*a) is called after the recursive call foo(a+1), the characters are printed in reverse order as the recursion unwinds.5.The stack of calls returns in the order: foo for 'D', then 'C', then 'B', then 'A'.6.The output is "DCBA".Turn this into a strength.Explore AI-powered practice and doubt support with Success Tracker.

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Correct answer(D) DCBASolutionThe function foo is a recursive function that processes a string character by character. 1.The base case for the recursion is when *a is either the null terminator \0 (evaluated as false in C) or a space character ' '.2.For the input "ABCD EFGH", the function calls itself recursively for 'A', then 'B', then 'C', then 'D'.3.When the pointer reaches the space character between 'D' and 'E', the condition *a != ' ' fails, and the recursion stops.4.Because putchar(*a) is called after the recursive call foo(a+1), the characters are printed in reverse order as the recursion unwinds.5.The stack of calls returns in the order: foo for 'D', then 'C', then 'B', then 'A'.6.The output is "DCBA".

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