I can't figure out how to use a "default value" when asking the user for input. I want the user to be able to just press Enter and get the default value. Consider the following piece of code, can you help me?
int number;
cout << "Please give a number [default = 20]: ";
cin >> number;
if(???) {
// The user hasn't given any input, he/she has just
// pressed Enter
number = 20;
}
while(!cin) {
// Error handling goes here
// ...
}
cout << "The number is: " << number << endl;
Use std::getline to read a line of text from std::cin. If the line is empty, use your default value. Otherwise, use a std::istringstream to convert the given string to a number. If this conversion fails, the default value will be used.
Here's a sample program:
#include <iostream>
#include <sstream>
#include <string>
using namespace std;
int main()
{
std::cout << "Please give a number [default = 20]: ";
int number = 20;
std::string input;
std::getline( std::cin, input );
if ( !input.empty() ) {
std::istringstream stream( input );
stream >> number;
}
std::cout << number;
}
This works as an alternative to the accepted answer. I would say std::getline is a bit on the overkill side.
#include <iostream>
int main() {
int number = 0;
if (std::cin.peek() == '\n') { //check if next character is newline
number = 20; //and assign the default
} else if (!(std::cin >> number)) { //be sure to handle invalid input
std::cout << "Invalid input.\n";
//error handling
}
std::cout << "Number: " << number << '\n';
}
Here's a live sample with three different runs and inputs.
if(!cin)
cout << "No number was given.";
else
cout << "Number " << cin << " was given.";
I'd be tempted to read the line as a string using getline() and then you've (arguably) more control over the conversion process:
int number(20);
string numStr;
cout << "Please give a number [default = " << number << "]: ";
getline(cin, numStr);
number = ( numStr.empty() ) ? number : strtol( numStr.c_str(), NULL, 0);
cout << number << endl;
