Example: Upper Triangular Matrix example in C++ using for loop

C
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// Upper Triangular Matrix example in C++ using for loop
#include <bits/stdc++.h>
using namespace std;

int main() {
    int size, flag = 0, i, j;

    cout << "Enter the size of the matrix: ";
    cin >> size;

    int matrix[size][size];

    cout << "\nEnter the matrix's elements:\n";
    for(i = 0; i < size; i++) {
        for(j = 0; j < size; j++)
            cin >> matrix[i][j];
        cout << endl;
    }

    for (i = 1; i < size; i++) {
        for (j = 0; j < i; j++) {
            if (matrix[i][j] != 0)
                flag = 0;
            else
                flag = 1;
        }
    }
  
    if (flag == 1)
        cout << "This is the Upper Triangular Matrix.\n";
    else
        cout << "This not an Upper Triangular Matrix!\n";

    return 0;
}