Zahra_matrix, C++ (gcc)

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//g++  5.4.0
// Created by Zahra Zaker Dehnavi

#include <iostream>
#include <cstdio>
#include <ctime>
using namespace std;

void Sub_Add(int a[][3], int b[][3], int sub[][3], int add[][3]) {
    const int n = 3;
    for(int i = 0; i < n; i++)
        for(int j = 0; j < n; j++) {
        sub[i][j] = a[i][j] - b[i][j];
        add[i][j] = a[i][j] + b[i][j];
    }
}

int main() {
    srand(static_cast<size_t>(time(0)));
    const int n = 3;
    int a[n][n];
    int b[n][n];
    int sub[n][n];
    int add[n][n];

/************* Phase 1 ************/
    // Filling and printing matrix a with random numbers
    cout << "Matrix A:\n";
    for (int (&i)[n] : a) {
        for (int (&j) : i) {
            j = rand() % 21; // [0, 20]
            cout.width(5);
            cout << j;
        }
        cout << endl;
    }

// Filling and printing matrix b with random numbers
    cout << "\nMatrix B:\n";
    for (int (&i)[n] : b) {
        for (int (&j) : i) {
            j = rand() % 21; // [0, 20]
            cout.width(5);
            cout << j;
        }
        cout << endl;
    }

/************* Phase 2 ************/
    Sub_Add(a, b, sub, add);

/************* Phase 3 ************/
    cout <<"\nSub[n][n] is:\n";
    for (const int (&i)[n] : sub) {
        for (const int (&j) : i) {
            cout.width(5);
            cout << j;
        }
        cout << endl;
    }

cout <<"\nAdd[n][n] is:\n";
    for (const int (&i)[n] : add) {
        for (const int (&j) : i) {
            cout.width(5);
            cout << j;
        }
        cout << endl;
    }
}

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Compilation time: 0.53 sec, absolute running time: 0.09 sec, cpu time: 0.02 sec, memory peak: 3 Mb, absolute service time: 0,63 sec