Calculate the square of the 3x3 two-norm

main.c

#include <stdio.h>

int main() {
    int matrix_A[3][3] = {0}, sum = 0;

    for (int i = 0; i < 3; ++ i)
        for (int j = 0; j < 3; ++ j)
            scanf("%d", &matrix_A[i][j]);

    for (int j = 0; j < 3; ++j)
        for (int i = 0; i < 3; ++i)
            sum += matrix_A[i][j] * matrix_A[i][j];

    printf("%d\n", sum);
    return 0;
}