Implicit return type int in C

In C, if a function is declared without an explicit return type, the compiler implicitly assumes the return type to be int. This behavior was allowed in older C standards (C89/C90) but is deprecated and not recommended. The C99 standard requires explicit return types for all functions.

Syntax

function_name(parameters) {
    /* Function body */
    return value;  /* Implicitly returns int */
}

Example: Implicit Return Type

Here's an example demonstrating implicit return type behavior −

#include <stdio.h>

my_function(int x) {
    return x * 2;
}

int main(void) {
    printf("Value is: %d<br>", my_function(10));
    return 0;
}

Value is: 20

Comparison: Implicit vs Explicit

Key Points

• Modern C compilers may issue warnings for functions without explicit return types
• Always specify return types explicitly for better code readability and portability
• The main() function should also have an explicit int return type

Conclusion

While implicit int return types were allowed in older C standards, modern programming practice requires explicit return type declarations. Always specify return types explicitly for better code clarity and standards compliance.