CODEWITHSUNDEEP
c++cin
Rob McNeil
Rob McNeil

Reputation: 61

Smarter way to implement this switch statement

So I am trying to allow a user to make a selection but Im having issue. the following lines 

cout << "\nWhat would you like to do? " << endl
    << "(1) Display the entire List" << endl
    << "(2) to exit" << endl;

getline(cin,answer);
answerint=stoi(answer);
switch (answerint) {
    case 1:
        showLIST(myLIst);
        break;
    case 2:
        return;
    default:
        cout << "\nPlease choose from the list";
   }

So this works fine if the user chooses a integer, but it barfs if a character is received. How can I make this less breakable?

Upvotes: 0

Views: 146

Answers (2)

Tony Delroy
Tony Delroy

Reputation: 106246

std::string answer;
int answerint;
while (std::getline(std::cin, answer))
{
    std::istringstream iss(answer);
    char c; // seek non-whitespace after the number?
    if (!(iss >> answerint) || (iss >> c))
        answerint = 0;
    switch (answerint)
    {
      ...as you had...
    }
}

The code above uses getline to ensure a complete line of text is parsed into answer, after which it creates a distinct std::istringstream from that single line. That way, we can use >> knowing it won't skip over newlines are consume or wait for further input.

if (!(iss >> answerint) || (iss >> c)) checks whether there isn't a number to parse into answerint, or after having parsed a number an additional non-whitespace character appears on the line. For example, the line typed might have been 2r - we'll consider that an error and reprompt for a selection, assigning 0 to answerint to ensure we reach the default label in the switch, thereby printing cout << "\nPlease choose from the list"; which seems as appropriate for 2r as for 99 or whatever....

Using getline and a separate istringstream this way, you can reliably attempt parsing of the next line of input from a known state.

Upvotes: 0

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

Reputation: 154035

It seems you want something like this:

if (std::cin >> answerint) {
    switch (answerint) {
        // ...
    }
}

Converting the integer directly from the stream puts the stream into failure state in case something different than an int is entered. You may want to add a manipulator to make sure there are no non-space characters on the end of the line.

Upvotes: 1

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