previous row element of array also getting updated - c++

Question

in this program i am separating integers from a character array which consists of a space between them
#include<iostream>
#include<stdio.h>
#include<conio.h>
using namespace std;
int main()
{
int i = 0, t, l = 0, j, c, k, q = 0, num = 0;
char ch[10][10];
int ach[10][1];
cout << "enter the number of test cases";
cin >> t;
for (i = 0; i < t; i++)
{
fflush(stdin);
cin.getline(ch[i], 9);
}
for (i = 0; i < t; i++)
{
num = 0;
for (j = 0; ch[i][j] != '\0'; j++) //calculating length
{
l = j;
}
l = l + 1;
for (j = 0; j < l; j++)
{
if (ch[i][j] == ' ') //finding the space
c = j;
}
for (k = 0; k < c; k++) //taking first integer out of char array
{
q = ch[i][k] - 48; //parsing char to int
num = (num * 10) + q;
}
cout << "\n previous row element " << ach[0][1] << "\n"; //checking the value
ach[i][0] = num; // this statement is updating the previous row's last element of the array
cout << "\n previous row element " << ach[0][1] << "\n"; //checking the value
cout << ach[i][0];
num = 0;
q = 0;
for (k = c + 1; k < l; k++) //taking second element out of char array
{
q = ch[i][k] - 48; //parsing char to int
num = (num * 10) + q;
}
ach[i][1] = num;
cout << ach[i][1];
}
for (i = 0; i < t; i++)
{
cout << "\n" << ach[i][0] << "\t" << ach[i][1] << "\n"; //displaying the values
}
getch();
return 0;
}
I have marked the code that is malfunctioning , it is updating the previous row's last element. please help.

Answer 1

Oups your code is not really optimized and is mainly C with the exception of cin.getline. But your real problem is that with int ach[10][1], ach is a 2D array of size 10x1, so ach[i][1] may not be what you expect because you should define int ach[10][2] to safely use it. The rules for array indexes computing give &(ach[i][1]) == &ach[0][0] + i*1 + 1 so you are actually accessing ach[i+1][0] with a possible past end array access if i is 9.
Moreover, at first access, ach[0][1] is used without being first initialized.
So your ach definition should be:
int ach[10][2] = {0};