Here's a C Program to find the sum of lower triangular elements of a matrix with explanation and example. This program uses Multidimensional Arrays, Nested Loops and For Loops.

Note: A lower triangular matrix is a square matrix in which the elements above the main diagonal are zero.

# include <stdio.h> # include <conio.h> void main() { int mat[10][10] ; int i, j, size, lower = 0 ; clrscr() ; printf("Enter size of the square matrix : ") ; scanf("%d", &size) ; printf("\nEnter the elements of the matrix : \n\n") ; for(i = 0 ; i < size ; i++) for(j = 0 ; j < size ; j++) scanf("%d", &mat[i][j]) ; printf("\nThe lower triangular matrix is : \n\n") ; for(i = 0 ; i < size ; i++) { for(j = 0 ; j < size ; j++) { if(j <= i) { printf("%d\t", mat[i][j]) ; lower = lower + mat[i][j] ; } else printf("\t") ; } printf("\n") ; } printf("\nThe sum of lower triangular elements is : %d", lower) ; getch() ; }

**Output of the above program**

Enter size of the square matrix : 3

Enter the elements of the matrix :

1 2 3

4 5 6

7 8 9

The lower triangular matrix is :

1

4 5

7 8 9

The sum of lower triangular elements is : 34

**Explanation of above program**

In this program, we have a square matrix

*mat*of maximum size 10 x 10. The variables i and j are the loop variables that corresponds to the row and column of the matrix respectively. The variable*size*contains the size of the matrix.
First
the program asks the user to enter the size of the matrix and then
using a nested for loops the matrix is populated. Now to get the lower triangular matrix, the program prints only those values in the matrix
for which

*j <= i*or column number is less than or equal to row number. Also the sum of lower triangular elements is also calculated and stored in the variable*lower.*Also take a look at: C Program to Find the Sum of Upper Triangular Matrix Elements