if else number and letters? C++

[BattleCrazy99]

I am trying to create a if else float on which when the user enters in a number value like 100.00 it should detect the users answer and if the user enters letters, then it should keep on repeating until the user puts a number in. But what is the fucntion or value that i have to use to do this, cause with my code now when I enter a word or letter it, bugs out and adds multiple lines in and tehn cuts the executible. whats the easy way of doing this.

float purchase;

std::cout << endl << "How much is the item you would like to
purchase: $"; //purchase enter text // we assume that the user enters
a valid score
std::cin >> purchase;

int main(){

if (!cin){ // figure out the purchase == no number value so loop works correctly
cin.clear(); // reset failbit
cin.ignore(std::numeric_limits<std::streamsize>::max());
cout << "Please select a state from the following list:";
}

else {
cout << "The entered cost is invalid..." << endl;
cout << endl << "How much is the item you would like to purchase: $";
cin >> purchase; // float value from the users price that was entered
}
}

[deleted account xyzzy]

#include <iostream>
#include <string>

double getInput();

int main()
{
   std::cout << "Enter a double: ";
   double input = getInput();

   std::cout << "\nYou entered " << input << '\n';
}

double getInput()
{
   double      input     = 0.0;
   std::string str_input = "";

   do
   {
      // retrieve the entire input and stuff it into a string
      std::getline(std::cin, str_input);

      try
      {
         // try to extract a double from the retrieved line of input
         // an error is thrown if not a double
         input = std::stod(str_input);

         return input;
      }

      catch (...)
      {
         std::cout << "Input error....try again: ";
         continue;
      }
   } while (true);

   return input;
}

Enter a double: hello
Input error....try again: 100.25

You entered 100.25

Enter a double: 5.75

You entered 5.75

Enter a double: a double
Input error....try again: try again
Input error....try again: error
Input error....try again: 100

You entered 100

[deleted account xyzzy]

A variation:

#include <iostream>
#include <string>

double getInput(const std::string&);

int main()
{
   double input = getInput("Enter a double: ");

   std::cout << "\nYou entered " << input << '\n';
}

double getInput(const std::string& query)
{
   double      input     = 0.0;
   std::string str_input = "";

   // ask the question
   std::cout << query;

   while (true)
   {
      // retrieve the entire input and stuff it into a string
      std::getline(std::cin, str_input);

      try
      {
         // try to extract a double from the retrieved line of input
         // an error is thrown if not a double
         input = std::stod(str_input);

         // the double was successfully retrieved, let's get out of here
         break;
      }

      catch (...)
      {
         std::cout << "Input error....try again: ";
         continue;
      }
   }

   return input;
}

Enter a double: hello
Input error....try again: 15.5

You entered 15.5