话说这也可以ac？

#include<bits/stdc++.h> using namespace std; typedef long long ll; int main() {//输出a*b%c ll a, b, c, ans; while (cin >> a >> b >> c) { ans = a * b % c; cout << ans << endl; } return 0; }

嗯同余~~(楼下说写题解加深印象)~~

#include<stdio.h>
#include<iostream>
using namespace std;
typedef long long ll;
int main()
{
	ll a,b,c,ans;
	while(cin>>a>>b>>c)
	{
		ans=((a%c)*(b%c))%c;
		cout<<ans<<endl;
	}
	return 0;
}

标准的同余

#include<cstdio>
#include<iostream>
using namespace std;
int main(){
	long long int a,b,c;
	while(cin>>a>>b>>c){
		a%=c;
		b%=c;
		long long int ans=a*b%c;
		printf("%lld\n",ans);
    }
    return 0;
}

//同余

#include<bits/stdc++.h>
using namespace std;
int main(){
	long long a,b,c,ans=0;
	while(scanf("%lld%lld%lld",&a,&b,&c)!=EOF){
		ans=((a%c)*(b%c))%c;
			cout<<ans<<endl;
	}
	return 0;
}