Clear Buffer

[Lucas Fiorini]

Hello,

I'm trying to prevent error from user input but when i check if the values are compatible into the if statement it always accept it as compatible types. How can I control the char input to only accept 'y'and 'n'? Thanks!

char answer;
    //wrong entry type prevention
    if(cin >> answer){
        cin.clear();
        cin.ignore(10000, '\n');
        cerr << "Inform your option again (y/n) ";
        cin >> answer;
    }
    
    int numberOfNodes;
    
    cout << "How many entries: ";

    //wrong entry type prevention
    if(!(cin >> numberOfNodes)){
        cin.clear();
        cin.ignore(10000, '\n');
        cerr << "Say again the amount of entries: ";
        cin >> numberOfNodes;
    }

[Ganado]

In your currently existing logic, how is the program supposed to know that 'y' and 'n' have different meanings than any other possible characters?

I would do something like this:

// Example program
#include <iostream>
#include <string>
#include <limits>

int main()
{
    using namespace std;
    
    char answer;
    cin >> answer;
    
    //wrong entry type prevention
    while (!cin || (answer != 'y' && answer != 'n')){
        cin.clear();
        cin.ignore(std::numeric_limits<streamsize>::max(), '\n');
        cerr << "Inform your option again (y/n) ";
        cin >> answer;
    }
    
    cout << "Your answer: " << answer << '\n';
    
    int numberOfNodes;
    cout << "How many entries: ";

    //wrong entry type prevention
    while (!(cin >> numberOfNodes)){
        cin.clear();
        cin.ignore(10000, '\n');
        cerr << "Say again the amount of entries: ";
        cin >> numberOfNodes;
    }
    
    cout << "Number of entries: " << numberOfNodes << '\n';  
}

[JLBorges]

#include <iostream>
#include <cctype>

bool answer_is_yes_to( const char* question )
{
    std::cout << question << "? [y/n]: " ;

    char ans ;
    std::cin >> ans ;
    ans = std::tolower(ans) ; // convert ans to lower case

    if( ans == 'y' ) return true ;
    if( ans == 'n' ) return false ;

    std::cout << "invalid input. try again\n" ;
    std::cin.ignore( 10000, '\n' ) ;
    return answer_is_yes_to(question) ;
}

int get_int( const char* prompt, int minv, int maxv )
{
    std::cout << prompt << " [" << minv << ',' << maxv << "]: " ;

    int number ;
    if( std::cin >> number )
    {
        if( number >= minv && number <= maxv ) return number ;
        else std::cout << "error: value " << number << " is out of range." ;
    }
    else std::cout << "error: non integer input." ;

    std::cin.clear() ; // clear a possible failed state
    std::cin.ignore( 1000, '\n' ) ; // discard this line of input
    std::cout << " try again\n" ;
    return get_int( prompt, minv, maxv ) ; // try again
}

int main()
{
    const bool angry = answer_is_yes_to( "are you angry" ) ;
    if(angry) std::cout << "cool down!\n" ;

    const int num_entries = get_int( "number of entries", 3, 8 ) ;
    std::cout << "num_entries == " << num_entries << '\n' ;
}