How to accept integer input values in different lines without using getline()?

Question

For example, I need to accept the dimensions of two rectangles on different lines.

I tried it this way:

int a1, b1, a2, b2;
char c;
cin >> a1 >> b1;
cin >> c >> a2 >> b2;

You cannot do this without using getline (or something equivalent). Can you explain why you can't use getline? — john, May 09 '20 at 06:48
If accepting it as a string no operations could be performed on the integral values.Values will be accepted with space and in different lines for different rectangles. — Saumya Chauhan, May 09 '20 at 06:53
The way to do this is to read the lines as a string and then **convert** the strings into integers. There are lots of different ways to convert strings into integers. — john, May 09 '20 at 06:58
But the easy way to do this is to write `cin >> a1 >> b1 >> a2 >> b2;` That will work if the input is on two lines, but it will also work if the input is on one line, or three lines or how ever many lines. Is that really a problem? — john, May 09 '20 at 07:00
``operator>>`` treats line breaks as ignorable whitespace, which is why `cin >> c` does not work to skip the line break. — Remy Lebeau, May 09 '20 at 07:05

Ardent Coder · Answer 1 · 2020-05-09T17:09:31.270

So you want the user to enter those 4 integers in this fashion:

-10 0
30 40

And you want to reject all other formats of input...

In other words, the input must include:

4 int integers
2 ' ' spaces
2 '\n' newlines

You can modify the logic I'm going to discuss to tweak those parameters as necessary.

This is more like a problem solving task. Anyways, since you don't want to use getline for some reason, you will have to manage most of the input processing yourself.

Here is my take on this:

Read the input character (char ch) by character until you receive four separate (separated by either a space or a newline) inputs (could be anything including void, validation can be done afterwards). Use std::stringstream (stringstream input) to read the entire input; it will make input validation easier as we proceed. Have two variables (unsigned spaceCount = 0; and unsigned newlineCount = 0;) to control the loop termination.
```
while (newlineCount + spaceCount != 4)
{
    ch = cin.get();
    input << ch;

    if (ch == ' ')
        ++spaceCount;

    if (ch == '\n')
        ++newlineCount;
}
```
Before proceeding, you need a function like bool isInt(string num) to check whether a given string is an integer or not. You can make one yourself according to your needs. Stackoverflow already has a thread on this: How to determine if a string is a number with C++? The function must return true only if the string can be fit into an int.

Then you can check the user-input for hidden gems, non-inputs or spam:

bool inputFormatCorrect = true;
if (spaceCount == 2 && newlineCount == 2)
{
    stringstream tmpInput;
    string tmpStr;
    tmpInput << input.str();
    for (int i = 0; i < 4; ++i)
    {
        tmpInput >> tmpStr;
        if (!isInt(tmpStr))
        {
            inputFormatCorrect = false;
            break;
        }
    }
}
else
{
    inputFormatCorrect = false;
}

Once the checking is complete, you can extract and display your integers (int a1, b1, a2, b2;):

if (inputFormatCorrect)
{
    input >> a1 >> b1 >> a2 >> b2;
    cout << "a1 = " << a1 << ", b1 = " << b1 << ", a2 = " << a2 << ", b2 = " << b2;
}
else
{
    cout << "I don't like your style of inputting...";
}

Putting it all together: Live Demo And I'm not really sure if you want the restriction on spaces as well, but you can modify the logic to remove all occurrences of spaceCount and change the read loop condition to while (newlineCount != 2) if required.

So, did you really mean to make things complicated? There's a reason why we have standard input.

I would still prefer

cin >> a1 >> b1 >> a2 >> b2;

Instead of giving the user a tough time:

How to accept integer input values in different lines without using getline()?

1 Answers1