Count the number of letter [C/C++]

#include<iostream>
#include<string>
using namespace std;

void main()
{
 char c;
 string str;
 int len, count = 0;

 cout << "Type the word you want: ";
 getline(cin,str);

 cout << "Type the letter you want to count: ";
 cin >> c;

 len = str.length();

 for (int ctr = 0; ctr < len; ctr++)
 {
 
  if (str.at(ctr) == c)
  {
   count = count + 1;
  }

 }

 cout << "\n";
 cout << "There are " << count << " letters in " << str << endl;

}