https://codewin.org/c-program-to-input-3x3-matrix-and-print-sum-of-all-elements/

3x3_matrix.c

#include<stdio.h>
#include<conio.h>
int main()
{
	int mat[3][3], i, j, sum;
	sum = 0;
	printf("Enter all 9 elements of 3*3 Matrix:-\n");
	for(i=0; i<3; i++)
	{
		for(j=0; j<3; j++)
		{
			scanf("%d", &mat[i][j]);
		}
	}
	for(i=0; i<3; i++)
	{
		for(j=0; j<3; j++)
		{
			sum = sum + mat[i][j];
		}
	}
	printf("\nSum of all elements = %d", sum);
	getch();

}