The reason the program goes into an infinite loop is because std::cin‘s bad input flag is set due to the input failing. The thing to do is to clear that flag and discard the bad input from the input buffer.

//executes loop if the input fails (e.g., no characters were read)
while (std::cout << "Enter a number" && !(std::cin >> num)) {
    std::cin.clear(); //clear bad input flag
    std::cin.ignore(std::numeric_limits<std::streamsize>::max(), 'n'); //discard input
    std::cout << "Invalid input; please re-enter.n";
}

See the C++ FAQ for this, and other examples, including adding a minimum and/or maximum into the condition.

Another way would be to get the input as a string and convert it to an integer with std::stoi or some other method that allows checking the conversion.

The top voted answer covers the solution really well.

In addition to that answer, this may help visualize what’s going on a little better:

int main()

    int input = 1;//set to 1 for illustrative purposes
    bool cinState = false;
    string test = "";
    while(input != -1){//enter -1 to exit
        cout << "Please input (a) character(s): ";//input a character here as a test
        cin >> input; //attempting to input a character to an int variable will cause cin to fail
        cout << "input: " << input << endl;//input has changed from 1 to 0
        cinState = cin;//cin is in bad state, returns false
        cout << "cinState: " << cinState << endl;
        cin.clear();//bad state flag cleared
        cinState = cin;//cin now returns true and will input to a variable
        cout << "cinState: " << cinState << endl;
        cout << "Please enter character(s): ";
        cin >> test;//remaining text in buffer is dumped here. cin will not pause if there is any text left in the buffer.
        cout << "test: " << test << endl;
    }
    return 0;    
}

Dumping the text in the buffer to a variable isn’t particularly useful, however it helps visualize why cin.ignore() is necessary.

I noted the change to the input variable as well because if you’re using an input variable in your condition for a while loop, or a switch statement it may go into deadlock, or it may fulfill a condition you weren’t expecting, which can be more confusing to debug.

Here is my approach to this matter.

Below is a C++ program that allows an end user to answer Yes or No to a simple “Yes” or “No” question.

This program will re-ask the same question, as long as the answer is neither Yes nor No.

Since C++ is case sensitive, I have also set up the program to accept both upper and lower case letters of the first letter of the allowed answers, since they both basically signify the same thing.

 #include <iostream>

 #include <string>

 using namespace std;

 int main() {
     
   string input;

   do {
       cout << "Are you interested in learning how to solve problems through coding?" <<endl;
       
       cout << "Choose Yes or No" <<endl;
       
       cin >> input;

       if ((input == "Yes") || (input == "yes"))
       
       {

        cout << "That is one of the ways of becoming a software engineer.";
        
        break;

       } 
       
       else if ((input == "No") || (input == "no"))
       
       {

        cout << "You have little possibility of becoming a computer engineer."<<endl;
        
        break;
        
       }

        } while ((input != "Yes" && input != "No") || (input != "yes" && input != "no"));

   return 0;
 }

Test the input to see whether or not it is what your program expects. If it is not, alert the user that the input they provided is unacceptable.

You can check it through the ASCII value if the ascii value s between 65 t0 90 or 97 to 122 the it would be character.