Simple program, but can't find the problem

[kethgr]

I wrote a program with a user-defined function that I want to tell me if the input letter is a vowel or not. When I run it and input a letter, it always returns that the letter is a vowel and I can't figure out why.
Here's what I have:

#include<iostream>

using namespace std;

bool isVowel(char letter);

int main()
{
char letter;

cout << "Please enter a letter: ";
cin >> letter;

if (isVowel(letter))
cout << letter << " is a vowel.";
else
cout << letter << " is a consonant.";

cout << endl << endl;

return 0;
}

bool isVowel(char letter)
{
if (letter == 'A' || 'a' || 'E' || 'e' || 'I' || 'i' || 'O' || 'o' || 'U' || 'u')
return true;
else
return false;
}

Thanks for your help.

[webJose]

You wrote the conditional as if you were writing plain English. Sorry, you have to repeat the variable and the comparison operator once for each letter.

if (letter == 'A' || letter == 'a' || letter == 'E' ...

In time you'll learn to do this check more efficiently.

[kethgr]

I sure hope so. :) Thanks for your help.