'For' loop problem involving i <= e Vs. i < e.

[Soneji]

Hello again!

Ok, I wrote the following program ( just messing around ), to find the exponent of a user's number.

Here's the problem:

If I place the less-than symbol ( < ) in the 'for' loop, it works fine.
However, the second I place the less-than or equal to operator ( <= ) in it's place, the code returns some crazy numbers.

I'm using: Win XP; & Dev-C++ 4.9.9.2;

Here's the code WITH the LToET operator:

#include <iostream>
using std::cout;
using std::endl;
using std::cin;
 
 
int main()
{
  int x = 0;
  int y = 1;
  int exp = 0;
  int choice = 0;
 
  cout << "Enter the base number: ";
  cin >> x;
  cout << endl;
 
  cout << "Now enter the exponent you want for " << x << ": ";
  cin >> choice; 
  cout << endl;              //    |   Here it is...
                                   //    V
  for (int index = 0; index <= choice; index++)
  {
    y *= x;
  }
 
  cout << x << "^" << choice << " = " << y << endl;
 
  return 0;
}
 

I must be missing something, because I didn't think there was much difference
between the two operators ( besides the obvious one of course 8^) ).

I appreciate any help anyone could give me. It's not a huge problem, but it is
a bit frustrating.

Thanks,

-Soneji

[JosAH]

If you want to raise x to the power of n you have to multply n x's so you have
to have a loop that executes its body n times; there are two choices:

for (int i= 0; i < n; i++) ...

or this one:

for (int i= 1; i <= n; i++) ... 

If you do this instead (what you did in your code):

for (int i= 0; i <= n; i++) ...

you effectively raise x to the power n+1.Note that overflow can cause funny
numbers too.

kind regards,

Jos

[cbbibleboy]

Also, if you just include math.h, there's an pow() function...

[Soneji]

Thanks for the reply!

I should have caught that. I haven't dealt with the <= operator much, but I think I've got it now.

Simply put: I was multiplying y times x as long as 'index' was "less than or equal to" 'choice'.

That "equal to" was giving me an extra iteration that I didn't need. Correct?

That's twice you've helped me JosAH, Thanks!

cbbibleboy, I haven't used 'math.h' much yet. But I'll look into it. Thanks!

Thanks again for your time,

Lates,

-Soneji