Program to print Lower triangular and Upper triangular matrix of an array

Given a two dimensional array, Write a program to print lower triangular matrix and upper triangular matrix.

  • Lower triangular matrix is a matrix which contain elements below principle diagonal including principle diagonal elements and rest of the elements are 0.
  • Upper triangular matrix is a matrix which contain elements above principle diagonal including principle diagonal elements and rest of the elements are 0.

Examples:

Input : matrix[3][3] = {1 2 3
                       4 5 6
                       7 8 9}
Output :
Lower : 1 0 0        Upper : 1 2 3
        4 5 0                0 5 6
        7 8 9                0 0 9

Input : matrix[3][3] = {7 8 9
                        3 2 1
                        6 5 4}
Output :
Lower : 7 0 0       Upper : 7 8 9
        3 2 0               0 2 1
        6 5 4               0 0 4

Steps:

  1. For lower triangular matrix, we check the index position i and j i.e row and column respectively. If column position is greater than row position we simply make that position 0.
  2. For upper triangular matrix, we check the index position i and j i.e row and column respectively. If column position is smaller than row position we simply make that position 0.
// CPP program to print Lower
// triangular and Upper triangular
// matrix of an array
#include<iostream>
using namespace std;
// Function to form lower triangular matrix
void lower(int matrix[3][3], int row, int col)
{
    int i, j;
    for (i=0; i<row; i++)
    {
        for (j=0; j<col; j++)
        {
            if (i<j)
            {
                matrix[i][j] = 0;
            }
            cout << matrix[i][j] << " ";
        }
        cout << endl;
    }
}
// Function to form upper triangular marix
void upper(int matrix[3][3], int row, int col)
{
    int i, j;
    
    for (i=0; i<row; i++)
    {
        for (j=0; j<col; j++)
        {
            if (i>j)
            {
                matrix[i][j] = 0;
            }
            cout << matrix[i][j] << " ";
        }
        cout << endl;
    }
}
// Driver function
int main()
{
    int matrix[3][3] = {{1, 2, 3}, {4, 5, 6}, {7, 8, 9}};
    int row = 3, col = 3;
    
    cout << "Lower triangular matrix: \n";
    lower(matrix, row, col);
    
    cout << "Upper triangular matrix: \n";
    upper(matrix, row, col);
        
    return 0;
}

Output:

Lower triangular matrix: 
1 0 0 
4 5 0 
7 8 9 
Upper triangular matrix: 
1 0 0 
0 5 0 
0 0 9 


Disclaimer: This does not belong to TechCodeBit, its an article taken from the below
source and credits.
source and credits:http://www.geeksforgeeks.org/program-print-lower-triangular-upper-triangular-matrix-array/
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rakesh

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