C++ input to Arrays Switches Variables Around

Question

I'm attempting to create a 3x3 table in C++, but the last value of each row is being replaced with the first value of the row above.

#include<iostream>
#include<iomanip>
#include<fstream>
using namespace std;



void fillArray(int *arrayRow1, int *arrayRow2, int *arrayRow3)
{
    cout << "Enter the number for row 1 column 1: " << endl;
    cin >> arrayRow1[0];
    cout << "Enter the number for row 1 column 2: " << endl;
    cin >> arrayRow1[1];
    cout << "Enter the number for row 1 column 3: " << endl;
    cin >> arrayRow1[2];

    cout << "Enter the number for row 2 column 1: " << endl;
    cin >> arrayRow2[0];
    cout << "Enter the number for row 2 column 2: " << endl;
    cin >> arrayRow2[1];
    cout << "Enter the number for row 2 column 3: " << endl;
    cin >> arrayRow2[2];

    cout << "Enter the number for row 3 column 1: " << endl;
    cin >> arrayRow3[0];
    cout << "Enter the number for row 3 column 2: " << endl;
    cin >> arrayRow3[1];
    cout << "Enter the number for row 3 column 3: " << endl;
    cin >> arrayRow3[2];


    cout << "Resulting Table:" << endl;
    cout << "_______" << endl;
    cout << "|" << arrayRow1[0] << "|"  << arrayRow1[1]  << "|" << arrayRow1[2] << "|" << endl;
    cout << "________" << endl;
    cout << "|" << arrayRow2[0] << "|"  << arrayRow2[1]  << "|" << arrayRow2[2] << "|" << endl;
    cout << "________" << endl;
    cout << "|" << arrayRow3[0] << "|"  << arrayRow3[1]  << "|" << arrayRow3[2] << "|" << endl;
    cout << "_______" << endl;
    
    
}

int main(){
int arrayRow1[2], arrayRow2[2], arrayRow3[2];
fillArray(arrayRow1, arrayRow2, arrayRow3);
}

When 1, 2, 3, 4, 5, 6, 7, 8, 9 is entered it resulting the the following output:

________
|1|2|4|
________
|4|5|7|
________
|7|8|9|
________

The expected output is:

________
|1|2|3|
________
|4|5|6|
________
|7|8|9|
________

What is cause this issue?

`int arrayRow1[2]` is an array with two elements. – 463035818_is_not_an_ai May 01 '22 at 18:10 — 463035818_is_not_an_ai, May 01 '22 at 18:10
Did you try stepping through the code with a debugger? – Quimby May 01 '22 at 18:12 — Quimby, May 01 '22 at 18:12

Odeaxcsh · Answer 1 · 2022-05-01T18:19:12.200

2

You are treating arrays as if they have three cells but you defined arrays with only two cells (e.g. arrayRow1[2]). This causes undefined behaviors which in this case I guess arrays are consecutive, and your indices kind of overlap. Change array definition to arrayRow[3] to fix the problem.

edited May 01 '22 at 18:19

answered May 01 '22 at 18:11

Odeaxcsh

133
7

score 1 · Answer 2 · answered May 01 '22 at 18:20

your int array rows only hold 2 elements each, so you should say

 int arrayRow1[3], arrayRow2[3], arrayRow3[3];

so they can hold 3 values each.

std::array should be used here, so you don't pass pointers to your function. For more efficient and cleaner code use multidimensional arrays [3][3] or std::array<std::array<int, 3>, 3>; in this case:

using table = std::array<std::array<int, 3>, 3>;

void fillArray(table& table)
{
    for (int row = 0; row < table.size(); ++row) {
        for (int col = 0; col < table[row].size(); ++col) {
            std::cout << "Enter the number for row " << row + 1 << " column " << col + 1 << ": " << std::endl;
            std::cin >> table[row][col];
        }
    }


    std::cout << "Resulting Table:" << std::endl;


    for (int row = 0; row < table.size(); ++row) {
        std::cout << "_______" << std::endl;
        std::cout << "|";
        for (int col = 0; col < table[row].size(); ++col) {
            std::cout << table[row][col] << "|";
        }
        std::cout << std::endl;
    }
}

int main() {
    table table;
    fillArray(table);
}

output:

Enter the number for row 1 column 1:
1
Enter the number for row 1 column 2:
2
Enter the number for row 1 column 3:
3
Enter the number for row 2 column 1:
4
Enter the number for row 2 column 2:
5
Enter the number for row 2 column 3:
6
Enter the number for row 3 column 1:
7
Enter the number for row 3 column 2:
8
Enter the number for row 3 column 3:
9
Resulting Table:
_______
|1|2|3|
_______
|4|5|6|
_______
|7|8|9|

read here why you shouldn't use namespace std;

C++ input to Arrays Switches Variables Around

2 Answers2