Работа с матрицами (нужно упростить функцию main)

#include <iostream>
using namespace std;
void P(double x[20][20], int N, double& S)
{
S=1;
for (int i=0; i<N; i++)
for (int j=0; j<N; j++)
if (j>i) S=S*x[i][j];}
int main()
{
int NA,NB,NC; 
double A[20][20],B[20][20],C[20][20];
double SA,SB,SC;
{
    cout<<"NA="; cin>>NA;
cout<<"Input Matrix A"<<endl;
for (int i=0; i<NA; i++)
for (int j=0; j<NA; j++)
cin>>A[i][j];
}
{
    cout<<"NB="; cin>>NB;
cout<<"Input Matrix A"<<endl;
for (int i=0; i<NB; i++)
for (int j=0; j<NB; j++)
cin>>B[i][j];
}
{
    cout<<"NC="; cin>>NC;
cout<<"Input Matrix A"<<endl;
for (int i=0; i<NC; i++)
for (int j=0; j<NC; j++)
cin>>C[i][j];
}
{P(A,NA,SA);
cout<<"SA="<<SA<<endl;
}
{P(B,NB,SB);
cout<<"SB="<<SB<<endl;
}
{P(C,NC,SC);
cout<<"SC="<<SC<<endl;
cout<<"Virazhenie="<<(SA+SB)*SC<<endl;
system("pause");}
}

...for (int j=i+1; j<N; j++)...