C Exercises: Find the sum of left diagonals of a matrix

Last update on September 27 2025 07:27:35 (UTC/GMT +8 hours)

24. Left Diagonal Sum

Write a program in C to find the sum of the left diagonals of a matrix.

The task is to write a C program that calculates the sum of the elements along the left diagonal of a square matrix. The program prompts the user to input the size of the matrix and its elements, computes the sum of the elements from the top-left to bottom-right diagonal, and displays both the matrix and the sum of its left diagonal elements as output.

Visual Presentation:

Sample Solution:

C Code:

#include <stdio.h>

int main() {
    // Declare variables and matrix
    int i, j, arr1[50][50], sum = 0, n, m = 0;

    // Display the purpose of the program
    printf("\n\nFind sum of left diagonals of a matrix :\n");
    printf("---------------------------------------\n");

    // Input the size of the square matrix
    printf("Input the size of the square matrix : ");
    scanf("%d", &n);

    m = n; // Storing the size of matrix for left diagonal traversal

    // Input elements into the matrix
    printf("Input elements in the matrix :\n");
    for (i = 0; i < n; i++) {
        for (j = 0; j < n; j++) {
            printf("element - [%d],[%d] : ", i, j);
            scanf("%d", &arr1[i][j]);
        }
    }

    // Display the matrix
    printf("The matrix is :\n");
    for (i = 0; i < n; i++) {
        for (j = 0; j < n; j++) {
            printf("% 4d", arr1[i][j]);
        }
        printf("\n");
    }

    // Calculate the sum of left diagonals
    for (i = 0; i < n; i++) {
        m = m - 1; // Decrementing to access elements on the left diagonal
        for (j = 0; j < n; j++) {
            if (j == m) {
                sum = sum + arr1[i][j]; // Adding elements on the left diagonal
            }
        }
    }

    // Display the sum of left diagonal elements
    printf("Addition of the left Diagonal elements is : %d\n", sum);

    return 0;
}

Sample Output:

Find sum of left diagonals of a matrix :                                                                      
---------------------------------------                                                                       
Input the size of the square matrix : 2                                                                       
Input elements in the first matrix :                                                                          
element - [0],[0] : 1                                                                                         
element - [0],[1] : 2                                                                                         
element - [1],[0] : 3                                                                                         
element - [1],[1] : 4                                                                                         
The matrix is :                                                                                               
   1   2                                                                                                      
   3   4                                                                                                      
Addition of the  left Diagonal elements is :5

Flowchart:

For more Practice: Solve these Related Problems:

• Write a C program to compute the sum of the secondary diagonal elements of a matrix.
• Write a C program to display the left diagonal of a matrix and then calculate the average of these elements.
• Write a C program to compute the left diagonal sum using pointer arithmetic on a 2D array.
• Write a C program to compute and compare the left and right diagonal sums of a square matrix.

Go to:

• C Array Exercises Home ↩
• C Programming Exercises Home ↩

PREV : Right Diagonal Sum.
NEXT : Sum of Rows & Columns.

C Programming Code Editor:

Click to Open Editor

Have another way to solve this solution? Contribute your code (and comments) through Disqus.