matrix multiplication

what is the algorithm for the product of two same size matrices?

heres the program of two 3x3 mat. I dug it up from some unknown hidden corner of my comp.

Code:

void mulofmatr(void)
{
 int a[3][3],b[3][3],c[3][3],i,j,p,q,x,y,pro,sum;
 clrscr();
  
 cout<<"ENTER ELEMENTS OF MATRIX A[3][3] :\n";
 for(i=0;i<3;i++)
  for(j=0;j<3;j++)
   cin>>a[i][j];

 cout<<"ENTER ELEMENTS OF MATRIX B[3][3] :\n";
 for(i=0;i<3;i++)
  for(j=0;j<3;j++)
   cin>>b[i][j];

 for(i=0;i<3;i++)
  for(j=0;j<3;j++)
  {
   p=i;
   q=0;
   x=0;
   y=j;
   sum=0;
   pro=1;
   while(q<=2)
   {
    pro=a[p][q]*b[x][y];
    sum=sum+pro;
    q=q+1;
    x=x+1;
   }
   c[i][j]=sum;
  }

  cout<<"\nELEMENTS OF MATRIX C AFTER MULTIPLICATION : ";
  for(i=0;i<3;i++)
 {
  cout<<'\n';
  for(j=0;j<3;j++)
  {
   cout<<c[i][j];
   cout<<"\t";
  }
 }

}