Question

In the following program, I am reading a 6-length string dd and storing its ascii code in an integer array ipc of size 3×2. The problem is that the values stored in ipc are wrong and they change themselves later when I reprint them. I am surprised how can there be such a clear problem with such a simple code. (I am using Code::Blocks 10.05 on Win7 x64)

#include<iostream>

using namespace std;

int main()
{ char dd[5];
  int ipc[2][1];
  cin.get(dd,6);
  for(int i=0;i<3;i++)
  { for(int j=0;j<2;j++)
    { ipc[i][j]=int(dd[j+2*i]);
      cout<<ipc[i][j]<<endl;
    }
  }
  cout<<"------"<<endl;
  for(int i=0;i<3;i++)
  { for(int j=0;j<2;j++)
    { cout<<ipc[i][j]<<endl; }
  }
}

If input given is 123456, the output is:

49
50
51
52
53
2
------
49
51
51
53
53
2

Any sort of help will be very much appreciated. Thank you.

Answer 1

The array declaration is incorrect and the code is going out-of-bounds on the array causing undefined behaviour. Declaration should be changed from:

int ipc[2][1]; 

to:

int ipc[3][2];

Additionally, cin.get() will read count - 1 characters, so:

cin.get(dd, 6);

will only read 5 characters, not 6. If the user enters 123456 only 12345 will be read. The cin.get() will also append a null character, (as commented by tinman). To correct increase the size of dd and the number of characters to be read:

char buf[7];
cin.get(buf, 7);