CODEWITHSUNDEEP
c++
user3395953
user3395953

Reputation: 19

Stopping the user from entering letters? C++

Hi i'm newish to C++ but i have a little problem which is i have to stop the user entering letters in a number section. I have made an attempt which works but its dodgy, because it will allow the user to continue then will tell them they have got something wrong and to restart the application. How do i validate it to bring up an error message telling them thats not a number and let them re enter a number?

Here is the code:

 double  Rheight;

do 
{
    cout << "Enter height of the room. " << endl;
    SetConsoleTextAttribute(GetStdHandle(STD_OUTPUT_HANDLE), 4);
    cout << "WARNING: If you enter a letter the program will exit." << endl; 
    SetConsoleTextAttribute(GetStdHandle(STD_OUTPUT_HANDLE), 7);
    cin >> Rheight;
}
while (Rheight > 20 || Rheight == 0);

Ask if you need to see more code.

Upvotes: 2

Views: 4491

Answers (2)

Dietmar K&#252;hl
Dietmar K&#252;hl

Reputation: 154045

There are basically two components to the answer:

  1. Detecting that the input failed.
  2. Cleaning up after a failed input.

The first part is rather trivial: you should always test after input that the stream is in a good state before using the input. For example:

if (std::cin >> value) {
    // use value
}
else {
    // deal with the input error
}

How to deal with the input error depends on your needs. When reading a file you'd probably abort reading the entire file. When reading from standard input you can ignore just the next character, the entire line, etc. Most like you'd want to ignore the entire line. Before doing so you'll need to put the stream back into a good state:

std::cin.clear();
std::cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n');

The first line clears the stream's error flags and the second line is a magic incantation ignoring as many characters as necessary until a newline got ignored.

Upvotes: 2

πάντα ῥεῖ
πάντα ῥεῖ

Reputation: 1

To check if the input was valid you can use

 if(!(cin >> Rheight))
 {
     cout << "Please input a valid number!" << endl;
     continue;
 }

Upvotes: 0

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