为啥这样计算不出来啊

#include<stdio.h>
int main()
{
    int a,b,c,m;
    int i,j,k;
    scanf("%d,%d,%d",&a,&b,&c);
    for(i=1;i<=m/3;i++)
    {
        for(j=1;j<=m/5;j++)
        {
            for(k=1;k<=m/7;k++)
            {
                if(3*i+a==5*j+b==7*k+c)
                {
                    m=3*i+a;
                }
            }
        }
    }
    printf("%d",m);
    return 0;
}

#include<iostream>
using namespace std;
int main() 
{
    int a = 0, b = 0, c = 0;
    cout << "输入a:";
    cin >> a ;
    cout << "输入b:";
    cin >> b;
    cout << "输入c:";
    cin >> c;
    for (int sum = 10; sum < 101; sum++)
    {
        if (sum % 3 == a && sum % 5 == b && sum % 7 == c)
        {
            cout << "总人数为：" << sum << endl;
            break;
        }
        else if (sum == 100)
        {
            cout << "无解" << endl;
        }
    }
    system("pause");
    return 0;
}