C PROGRAMMING PROGRAM • MATRICES

Find Primary and Secondary Diagonal Sums

Learn how to find primary and secondary diagonal sums using a clear C program.

IntermediateSquare matrixDiagonalsIndex relationship

PROBLEM UNDERSTANDING

Input and expected output

Sample input

Sample output

Primary diagonal sum = 15
Secondary diagonal sum = 15

COMPLETE C PROGRAM

Complete C implementation

#include <stdio.h>

int main(void)
{
    int size, matrix[10][10], primary = 0, secondary = 0;

    scanf("%d", &size);
    if (size < 1 || size > 10) return 1;
    for (int row = 0; row < size; row++)
        for (int column = 0; column < size; column++) scanf("%d", &matrix[row][column]);
    for (int index = 0; index < size; index++) {
        primary += matrix[index][index];
        secondary += matrix[index][size - index - 1];
    }
    printf("Primary diagonal sum = %d\nSecondary diagonal sum = %d\n", primary, secondary);
    return 0;
}

CURRENT STEP

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EXPECTED OUTPUT FOR THE SAMPLE

Primary diagonal sum = 15
Secondary diagonal sum = 15

0%Step 0 of 0

PROGRAM EXPLANATION

Algorithm and explanation

Read the required input values.
Use indices (i,i) for the primary diagonal and (i,n−i−1) for the secondary diagonal.
Display the computed result.

Use indices (i,i) for the primary diagonal and (i,n−i−1) for the secondary diagonal.

EFFICIENCY

Time and space complexity

Time complexity

O(n)

Auxiliary space

O(rows × columns)

DEBUGGING CHECKLIST

Common mistakes

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Use the correct format specifier for every variable.

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Initialize variables before using their values.

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Check braces, semicolons and input order carefully.

Try it yourself

Practice: Run the program with the sample input, predict its output, and then test one boundary case of your own.