c - call to undefined function in function main()

Question

whenever i use a function which is called in main function, it gives this error: Call to undefined function in function main() i am using turbo c++ compiler version 4.5 and windows vista ultimate service pack 2 Can you tell which header file or something else is to be used. I am beginner in C language.

An example which produces this error:

#include<stdio.h> 

main( ) 
{ 
  int i ; 
  int marks[ ] = { 1, 2, 3, 4, 5, 6, 7 } ; 

  for ( i = 0 ; i <= 6 ; i++ ) display ( marks[i] ) ; 
} 

display ( int m ) 
{ 
  printf ( "%d ", m ) ; 
}

Answer 1

You need to define (or at least declare) any function before use. You can do that by including a header that includes a declaration (or prototype) for the function, or the declaration or definition can be contained directly in the source file at hand. For example:

#include <stdio.h>

void doit() { 
    // call function declared in <stdio.h>
    printf("Function called from main");
}

int main() {
    // call function defined above.
    doit();
    return 0;
}