/* Version using global vars... */

#include <stdio.h>
#include <ctype.h>
#include <string.h>

#define TRUE (1)
#define FALSE (0)

double xsum, ysum;


int strequal(char s0[], char s1[])
{
  return(strcmp(s0, s1) == 0);
}

void complex_add(
  double x1, double y1,
  double x2, double y2)
{
  xsum = x1 + x2;
  ysum = y1 + y2;
}


void main(void)
{
  int done;
  char answer[80];
  double x1, y1, x2, y2; 

  printf("Welcome to CADD.\n\n");
  done = FALSE;
  while (!done)
  {
    printf("Please enter x1: ");
    scanf("%lf", &x1);
    printf("Please enter y1: ");
    scanf("%lf", &y1);

    printf("Please enter x2: ");
    scanf("%lf", &x2);
    printf("Please enter y2: ");
    scanf("%lf", &y2);
 
    complex_add(x1, y1, x2, y2); 

    printf("The sum is: %f + j %f\n\n", xsum, ysum);

    printf("Do another (y/n)? ");
    scanf("%s", answer);
    done = strequal(answer, "n");
  }

  printf("Goodbye from CADD.");
}