Error in pari/gp code

["Swati, NoFirstName" <S10@email.sc.edu>]

Hi,

I am trying to write a code to output the position of the last non-zero entry of this matrix but the code is giving a syntax error. I am not sure what went wrong. Could someone help in this regard?

Thanks,

Swati 

C = [[1, 2, 3, 4], [7, 9, 10], [25, 31, 0], [0, 0, 0]];

A = matconcat([C[1]; C[2]; C[3]; C[4]]);

R = 0;

C = 0;

S= 0;

for(i = matsize(A)[1], i >= 1 &&  S == 0, i--,

    for(j = matsize(A)[2], j >= 1 &&  S== 0, j--,

        if(A[i, j] != 0,

            R = i;

            C = j;

           S = 1; 

            break; 

  )))

if(S == 1,

    print("Position of the last non-zero entry:" [R, C]), 

    print("Matrix A contains only zeros.")

);