Multiplying two matrix in c++

Question

I'm trying to multiply two matrix in c++ but result not correct!
Could you please let me know what's wrong with ,my code?!

#include<iostream>
#include <stdio.h>
#include <stdlib.h>
#include <omp.h>
//more detail
using namespace std;
#define WIDTH1 3
#define HEIGHT1 3
#define WIDTH2 3
#define HEIGHT2 3
#define WIDTH3 3
#define HEIGHT3 3
int A[HEIGHT1][WIDTH1];
int B[HEIGHT2][WIDTH2];
int C[HEIGHT3][WIDTH3];
int n, m;
int y = 0;
//more detail :)

int main() {
    for (int i = 0; i < 3; i++)
        for (int j = 0; j < 3; j++)
        {
            cin >> m;
            A[i][j] = m;
        }
    for (int i = 0; i < 3; i++)
        for (int j = 0; j < 3; j++)
        {
            cin >> n;
            B[i][j] = n;
        }
//more detail :)

    for (int i = 0; i < 3; i++) 
    {
        int k = 0;
        int sum = 0;
        int sum2 = 0;
        int sum3 = 0;
        for (int j = 0; j < 3; j++)
        {
            int sum = A[i][j] * B[j][i];
            sum += sum; 
        }
        B[i][y] = sum;
        y = y + 1;
        for (int j = 0; j < 3; j++)
        {
            int sum2 = A[i][j] * B[j][i];
            sum2 += sum2;
        }
        B[i][y] = sum2;
        y = y + 1;
//more detail :)

        for (int j = 0; j < 3; j++)
        {
            int sum3 = A[i][j] * B[j][i];
            sum3 += sum3;
        }
        B[i][y] = sum3;
        y = y + 1;
    }
    for (int i = 0; i < 3; i++)
        for (int j = 0; j < 1; j++)
        {
            cout << B[i][j] <<"\t" << B[i][j+1] << "\t" << B[i][j+2] << "\n" ;
        }
    return 0;
//more detail :)

}

Answer 1

What do you think this does:

    for (int j = 0; j < 3; j++)
    {
        int sum = A[i][j] * B[j][i];
        sum += sum; 
    }

in relation with your original sum? It doesn't do anything.

Don't redeclare the same variable.

    for (int j = 0; j < 3; j++)
    {
        sum += A[i][j] * B[j][i];
    }