Detecting return key

I want to simplify user input of parameters to a programme by offering default values - ie if the user just presses Return the default value is assigned. The input section should be something like this:

Code:

float sym_size;

cout << "Input symbol size in cm (default = 0.1cm): ";
cin >> sym_size;

if (xxxxxxxxxxxxxxxx)
{
  sym_size = 0.1;
}

The problems are

1. the programme seems to hang if you just press return

2. I don't know what to put in for the if condition to test for pressing return with no other input

Is there a smart way of doing this?

You use cin.getline() to read the input into a string.

If that line begins with a newline, then assign the default value, otherwise convert the value in the string to a float.

string streams are a good idea here

I don't think you can do that with cin. I tried it and when you just hit return it still waits for user input. Now if there is a way to make cin accept just hte return key the string it returns should be either "\n\0" or "\0". So your if statement would be one of these:

Code:

if (sym_size[0] == '\0')
{//blank input

Code:

if ((sym_size[0] == '\n')&&(sym_size[1] == '\0')
{//blank input

Alternatively you can use the getch() function which returns after a single keypress to get the input. You'll need to place it in a loop to actually get the input:

Code:

char input[512];
int ctr;

for (ctr = 0; ctr < 512; ctr+)
{
    input[ctr] = getch();
    //getch() won't echo the character to screen
    printf("%c", input[ctr]);

    if (input[ctr] == '\n')
    {//the user hit return, stop getting characters
        break;
    }

    if (input[ctr ] == '\b')
    {//user hit backspace, remove a character
        ctr -= 2;
    }
}

if (input[0] == '\0')
{
    //user didn't give a value insert the default
}

You may need to clean that up a bit, but that should give you an idea how it would look.

FYI: getch() only exists on windows (include conio.h) there is a good tutorial on the board somewhere (I seem to have lost the link) to get it to work on Linux if need be.

Use cin.peek() in a while loop. Here's an example..

Code:

#include <iostream>
using namespace std;

int main()
{
	int userInput = 0;
	
	cout << "Input data: ";

	while (cin.peek() != '\n')
		cin >> userInput;
	
	if ( userInput )
	{
		cout << userInput;
		while (cin.get() != '\n'); // flush stream after input //
	}
	else
	{
		cout << "Enter pressed.";
		cin.ignore();  // flush the \n that was just pressed //
	}
	
	cin.get(); // keep console window open until enter pressed //
	return 0;
}

cin.peek() returns the next character from input without extracting it from the input stream.