Formatting columns in C++

Question

I have the following program that generates a multiplication table. A formatting problem arises when the outputs reach the double digits. How do I straighten out the columns?

#include <iostream>

using namespace std ;
int main() 
{
  while (1 != 2)
  {
    int column, row, c, r, co, ro; 

    cout << endl ;

    cout << "Enter the number of columns: " ;
    cin >> column ;
    cout << endl ;
    cout << "Enter the number of rows:    " ;
    cin >> row ;
    cout << endl ;

    int temp[column] ;
    c = 1 ; 
    r = 1 ; 
    for(ro = 1; ro < row ; ro ++ ){
      for(co = 1; co < column ; co ++ ){
            c = c ++ ;
            r = r ++ ;
            temp [c]= co * ro;

            cout << temp[c] << " ";
      }
      cout << endl ;
    }
    system("pause");  
  }
}

Answer 1

C++ had setw and setfill for just this purpose. setw sets the width and setfill sets the fill character.

In your case, you can just use something like:

#include <iostream>
#include <iomanip>

int main (void) {
    std::cout << std::setw(5) << 7 << std::endl; // will output "    7".
    return 0;
}

---

You have a number of other problems with that code, at least some of which are listed below:

• You don't allocate enough space for your array, it should be column*row (or use a two-dimensional array).
• Array indexes start at 0, not 1.
• c = c++ is not a good idea, c++ will be enough to increment c.
• You may be trying to increment c twice in each iteration, once if the for statement itself and once in the for body.
• system("pause"); is an ugly hack where the language provides a perfectly good getchar or cin equivalent.
• while (1 != 2) just looks plain wrong :-) since 1 will never equal 2. Just use while (1) or for(;;) - any coder worth their salt will know what you mean.

Answer 2

This is one of those situations where the old-fashioned printf is a lot easier than cout. Replace cout << temp[c] << " " with printf("%2d ", temp[c]).

And I hope you've discovered the bug in your c calculation.

Answer 3

You can set width of your column elements by using stream manipulators like this:

cout << setw(3) << temp[c]

But this is something you need to fix besides: c = c++; does not increment the variable!

Answer 4

use the setw output manipulator:

cout << setw(3) << temp[c];

By default, this uses spaces to fill, which it looks like you want.

You will need to include iomanip as the documentation says.

Answer 5

You could use "\t" instead of " ".