C Language | Functions | Function Declarations

Tags:

A function declaration tells the compiler a function’s name, return type, and parameter types without defining its body.

Function Prototypes

Declare a prototype before calling a function whose definition appears later.

return_type function_name(parameter_list);

#include <stdio.h>

void CharLoop(char chMark, int iNum);

int main(void) {
  CharLoop('*', 30);
  printf("\n---\n");
  CharLoop('*', 40);
  printf("\n");
  return 0;
}

void CharLoop(char chMark, int iNum) {
  int iCount;
  for (iCount = 0; iCount < iNum; iCount++)
    printf("%c", chMark);
}

Modern code should use prototypes. For a function with no parameters, write void explicitly.

void Function(void);

Writing void Function(); does not declare a no-parameter prototype in C. It declares a function with unspecified parameters.

Omitting Parameter Names

Names are optional in a prototype because only the types are required.

void Function(int, char, double);
void CharLoop(char chMark, int);

Parameter names are still useful when they clarify the purpose of each value.