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;
}

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