ACM PKU 3318 Matrix Multiplication http://acm.pku.edu.cn/JudgeOnline/problem?id=3318

#include <iostream>
using namespace std;
int main ()
{
    int n;
int a[500][500],b[500][500],c[500][500];
cin>>n;
for (int j1=0;j1<n;j1++)
    for (int k1=0;k1<n;k1++)
     scanf("%d",&a[j1][k1]);
for (int j2=0;j2<n;j2++)
    for (int k2=0;k2<n;k2++)
     scanf("%d",&b[j2][k2]);
for (int j3=0;j3<n;j3++)
    for (int k3=0;k3<n;k3++)
     scanf("%d",&c[j3][k3]);
for (int nn=0;nn<n;nn++)
   for (int mm=0;mm<n;mm++)
   {
    int sum=0;
    for (int ll=0;ll<n;ll++)
    sum=sum+a[nn][ll]*b[ll][mm];
    if (sum!=c[nn][mm])
    {
     cout<<"NO"<<endl;
     return 0;
    }
   }
   cout<<"YES"<<endl;
return 0;
}