// AP Computer Science, A Exam, 1996, Question 4, part A in C++
// also AB Exam, question 2

int SumCross(const Matrix<int> & m, int R, int C)
// precondition: 0 <= R < m.numRows(); 0 <= C < m.numCols()
{
    int sum = 0;
    int j;

    int rows = m.numRows();        // store value, call only once
    int cols = m.numCols();        // per loop iteration

    // sum down the C-th column
    
    for(j=0; j < rows; j++)
    {
	sum += m[j][C];
    }

    // sum across the R-th row

    for(j=0; j < cols; j++)
    {
	sum += m[R][j];
    }

    // subtract m[R][C] which was summed twice

    sum -= m[R][C];

    return sum;
    
}