Remove all the vowels from a string

This is the instructions for the program I have to write:
Write a program that prompts the user to input a string. The program then uses the function substr to remove all the vowels from the string. For example, if str = "There", then after removing all the vowels, str = "Thr". After removing all the vowels, output the string. Your program must contain a function to remove all the vowels and a function to determine whether a character is a vowel.

With that being said, this is the program I have written. I am not sure if it is correct or not though and I was wanting to seek help on it. Any pointers would be greatly appreciated.

Code:

int main()
{
   string str;
   void removeVowels(string str);   
   
   cout << "Enter a string: ";
   cin >> str;
   cout << endl;

   cout << "The new string is: " << removeVowels << endl;
   
   cout << "\nThe stringafter the function is: " << str << endl;
   return 0;
}

bool isVowel(char ch)
{
      if ((ch=='A')||(ch=='E')||(ch=='I')||(ch=='O')||(ch=='U')
         ||(ch=='a')||(ch=='e')||(ch=='i')||(ch=='o')||(ch=='u'))
   {
      cout << isVowel << endl;
      return true;
   }
      else
   {
      return false;
   }
   {
      cout << str.substr(isVowel) << endl;
   }
   return 0;
}