记得x和y的坐标都是实数类型而不是整数。

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


int main(){
	double x1,x2,y1,y2;
	double juli;
	while(scanf("%lf,%lf,%lf,%lf",&x1,&y1,&x2,&y2)!=EOF){
		juli=sqrt((y2-y1)*(y2-y1)+(x2-x1)*(x2-x1));
		printf("%.2f\n",juli);
	}
	return 0;
}

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

int main(){
	double tot[100][4];
	
	int i=0;
	while(scanf("%lf,%lf,%lf,%lf",&tot[i][0],&tot[i][1],&tot[i][2],&tot[i][3])!=EOF){
		double t=sqrt((tot[i][0]-tot[i][2])*(tot[i][0]-tot[i][2])+(tot[i][1]-tot[i][3])*(tot[i][1]-tot[i][3]));
		printf("%.2lf\n",t);
		i++;
	}				
   
   
   
	return 0;
}

#include <iostream>
#include <cstring>
#include <cmath>
#include <vector>
#include <cstdio>
using namespace std;
int main()
{
    string str;
    while(cin >> str)
    {
        vector<int> coord;
        int num = 0;
        for (size_t i = 0; i < str.size(); i++)
        {
            if (str[i] == ',')
            {
                coord.push_back(num);
                num = 0;
                continue;
            }
            num = num * 10 + str[i] - 48;
        }
        coord.push_back(num);

        int x = abs(coord[2] - coord[0]),
            y = abs(coord[3] - coord[1]);
        
        double ans = sqrt(x * x + y * y);

        printf("%.2f\n", ans);
    }
    return 0;
}

#include<bits/stdc++.h> using namespace std;

//double x1,y1,x2,y2; 要是在这里声明变量 OJ会报错 但是自己测试答案是正确的 也不知道为什么

double ans;

void juli(double x_1,double y_1,double x_2,double y_2) { ans=sqrt((x_1-x_2)(x_1-x_2) + (y_1-y_2)(y_1-y_2)); printf("%.2f\n",ans); }

int main() { double x1,y1,x2,y2;

while(scanf("%lf,%lf,%lf,%lf",&x1,&y1,&x2,&y2)!=EOF)
{
	juli(x1,y1,x2,y2);
}
return 0;

}