Question

I have to do an exercise for University that asks me to check ( for k times ) if a matrix has positive rows ( i mean a row with all positive elements ) , i think there’s something wrong with the indices of for loops but i cannot find the mistakes.

i tried to debug with a cout statement apply to the counter an it gives me “101” , so it seems like compiler assign “1” to the positive rows and “0” to the negative

This is the code i wrote:

#include <iostream>

using namespace std;

const int N = 3;

bool positive(int a[N][N], int row[N], int x) {
    bool condition = false;

    for(int i = 0; i < N; i++) {
        row[i] = a[x][i];
    }

    int j = 0;

    while(j < N) {
        if(row[j] >= 0) {
            condition = true;
        } else {
            condition = false;
        }

        j++;

    }

    return condition;
}


bool function (int a[N][N], int z, int j, int k) {
    int b[N];
    int c[N];
    int count = 0;

    if(positive(a, b, z) && positive(a, c, j)) {
        count++;
    }

    if(count == k) {
        return true;
    } else {
        return false;
    }
}


int main() {
    int a[N][N] = {
        {
            2, 8, 6
        }, {
            -1, - 3, - 5
        }, {
            6, 10, 9
        }
    };

    int k = 2;

    for(int i = 0; i < N; i++) {
        for(int j = 0; j < N; j++) {
            if(function (a, i, j, k)) {
                cout << "OK";
            } else {
                cout << "NO";
            }

        }
    }

    return 0;
}

Answer 1

You should probably take another look at this problem and restart with a different solution. The objective is pretty easy but your code is surprisingly complex and some of it doesn’t really make sense.

For example, if you had a matrix like this:

    1   2   4    --> matrix A
   -1   8  -6
    3   9   2

You have N=3 rows and columns. The only thing you have to to based on what you said is take the matrix, cycle through the N rows, and for each row, check it’s N columns to see if anything is < 0.

Doing this K times, as you put it, makes no sense. The matrix will be the same every time you compare it since you’re not changing it, why would you do it more than once? I think you should reread the assignment brief there.

As for the logic of finding which rows are positive or negative, just do something simple like this.

//Create array so we have one marker for each row to hold results.
bool rowPositiveFlags[N] = { true, true, true };

//Cycle through each row.
for (int row = 0; row < N; ++row)
    //Cycle through every column in the current row.
    for (int col = 0; col < N; ++col)
        //If the column is negative, set the result for this row to false and break
        //the column for loop as we don't need to check any more columns for this row.
        if (A[row][col] < 0) {
            rowPositiveFlags[row] = false;
            break;
        }

You should always name things so that you can read your code like a book. Your i’s, j’s, and k’s just make something simple confusing. As for the problem, just plan out your solution.

Solve the problem by hand on paper, write the steps in comments in your code, and then write code below the comments so what you do definitely makes sense and isn’t overkill.

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And this is a great site, but next time, post a smaller piece of code that shows your problem. People shouldn’t ever give you a full solution here for homework so don’t look for one. Just find the spot where your indices are broken and paste that set of 5 lines or whatever else is wrong. People appreciate that and you’ll get faster, better answers for showing the effort 🙂