Making function calls

/* 1501.c: Making function calls */
#include <stdio.h>

int function_1(int x, int y);
double function_2(double x, double y)
{
printf("Within function_2.\n");
return (x - y);
}

main()
{
    int x1 = 80;
    int y1 = 10;
    double x2 = 100.123456;
    double y2 = 10.123456;

    printf("Pass function_1 %d and %d.\n", x1, y1);
    printf("function_1 returns %d.\n", function_1(x1, y1));
    printf("Pass function_2 %f and %f.\n", x2, y2);
    printf("function_2 returns %f.\n", function_2(x2, y2));
    return 0;
}
/* function_1() definition */
int function_1(int x, int y)
{
    printf("Within function_1.\n");
    return (x + y);
}