Char test

#include <iostream>
#include <string>
using std::cin;
using std::cout;
using std::endl;

int main(){
  char phrase[100];
  int vocala=0;
  cout<< "Write a phrase" << endl;
  cin.getline(phrase,100);
  cout << "which letter do you want to count? " << endl;
  char a=0;
  cin >> a;
  for (int i=0;i<100;i++)
    {
      if(phrase[i] == a)
        {
            vocala=vocala++ + 1;
        }
    }

  cout << "the numbers of letters " << a << " in this phrase is: " << vocala << endl;

  return 0;
}