c语言编写函数实现求两点间的距离。主函数输入两个点的坐标，调用函数求出两点的距离。

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

float distance(float x1, float y1, float x2, float y2) {
    float dist = sqrt((x2 - x1) * (x2 - x1) + (y2 - y1) * (y2 - y1));
    return dist;
}

int main() {
    float x1, y1, x2, y2, dist;
    printf("Enter the coordinates of point 1: ");
    scanf("%f %f", &x1, &y1);
    printf("Enter the coordinates of point 2: ");
    scanf("%f %f", &x2, &y2);
    dist = distance(x1, y1, x2, y2);
    printf("The distance between the two points is: %f\n", dist);
    return 0;
}

该程序中，`distance()`函数计算两点之间的距离，需要四个参数，分别为两个点的x和y坐标。主函数中通过`scanf()`函数获取两个点的坐标，然后调用`distance()`函数计算距离并输出结果。