#include <stdio.h>
#include <math.h>

/* Find the roots a * x*x + b * x + c = 0 */
void solveQuadraticEquation(void){
  /*  ... */
}   

int main(void) {
  solveQuadraticEquation();   
  /* OK: solveQuadraticEquation now known to the compile */
  return 0;
}