Implicit return type int in C

Predict the output of following C program.





#include <stdio.h>
fun(int x)
    return x*x;
int main(void)
    printf("%d", fun(10));
    return 0;


Output: 100

The important thing to note is, there is no return type for fun(), the program still compiles and runs fine in most of the C compilers. In C, if we do not specify a return type, compiler assumes an implicit return type as int. However, C99 standard doesn’t allow return type to be omitted even if return type is int. This was allowed in older C standard C89.

In C++, the above program is not valid except few old C++ compilers like Turbo C++. Every function should specify the return type in C++.

This article is contributed by Pravasi Meet. Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above

Don’t stop now and take your learning to the next level. Learn all the important concepts of Data Structures and Algorithms with the help of the most trusted course: DSA Self Paced. Become industry ready at a student-friendly price.

My Personal Notes arrow_drop_up
Article Tags :
Practice Tags :


Please write to us at to report any issue with the above content.