C Program to Find the Sum of Lower Triangular Matrix Elements

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