I'm confused

I have to creat 2 matrices and then produce a third matrxi. But here is the problem that i have:

Question states "third matrix whose all off diagonal entries are zero and the diagonal entries are the sum of first 2 matrices."

Off diagonal? diagonal? I dotn get that

1 3 5

5 6 7

7 9 9

would diagonal be 1,6 and 9? and the rest off diagonal?

and then i'm not really sure how to add them...so far i have:

Code:void get_mat(int mat[][3]); void get_mat2(int matx[][3]); void add_mat(int mat1[][3], int mat2[][3], int mat3[][3]); void ptr_mat(int mat[][3]); main() { int matrix[3][3]; int matrix1[3][3]; int matrix2[3][3]; get_mat(matrix); get_mat2(matrix1); add_mat(matrix, matrix1, matrix2); ptr_mat(matrix2); } void get_mat(int mat[][3]) { int i, j; for(i=0; i<3; i++){ for(j=0; j<3; j==){ printf("Please enter Matrix 1 [%d][%d]", i,j)' scamf("%d", &mat[i][j]); } } } void get_mat(int mat2[][3]) { int i, j; for(i=0; i<3; i++){ for(j=0; j<3; j==){ printf("Please enter Matrix 1 [%d][%d]", i,j)' scamf("%d", &mat2[i][j]); } } }

thanks