Vowel words counter C++

#include <iostream>
using namespace std;

void main(){
int c = 0;
char a[100];
cin >> a;
for (int i = 0 ; i<100; i++){
if (a[i] == 'a' || a[i] == 'e' || a[i] == 'i' || a[i] == 'o' || a[i] == 'u') {
c++;
}
}
cout << c << endl;
}