Test converted int to char if it is number c++

Question

I would like to know how to test if a char is a number. An int has been converted to char and later on I want to see if this char is a number.

int num = 2;
char number = '2';
char num2 = (char)num;
cout << "Non comverted: " << number << " " << num2 << endl;
cout << "comverted: " << static_cast<int>(number) << " " << static_cast<int>(num2) << endl;
if (isdigit(number))
  cout << "number" << endl;
else if (isdigit(num2))
  cout << "num2" << endl;
else cout << "none" << endl;

when I run this the second if should also be able to relate to true.

The reason why I want to be able to do this is because I store a lot of different values into a char array and would later like to know when something is a number or not.

Thanx a lot

score 0 · Answer 1 · answered Oct 10 '14 at 14:16

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To translate single digits from int to ascii/utf8 characters there is a very simple conversion:

char num2 = static_cast<char>('0' + num);

answered Oct 10 '14 at 14:16

Oliver

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score 0 · Answer 2 · answered Oct 10 '14 at 14:16

This:

char num2 = (char)num;

Does not make sense. You're casting a 2 to a char which will give you ASCII code for STX, a special character (http://www.asciitable.com/).

You probably want this:

char num2 = '0' + num;

What that does is give you a character counted from ASCII '0', so it will work up to 9, after which you will get other characters as seen in the ASCII table.

score 0 · Accepted Answer · edited May 23 '17 at 10:33

0

You aren't actually converting num to a number. Your line 3 basically results in:

char num2 = (char)2;

The ASCII character with decimal value 2 is not a digit. In fact, it is not printable. The easiest way to convert a single digit integer to its printable char is to add '0' to it:

char num2 = '0' + num;

The reason for this is that the character 0 is the first digit in the ASCII table, directly followed by 1, 2, 3, etc...

Edit

As Christian Hackl points out in the comments, c++ does not require an implementation to use ASCII, although it is guaranteed that the digits 0 through 9 are represented by contiguous integer values.

edited May 23 '17 at 10:33

Community

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answered Oct 10 '14 at 14:20

Bart van Nierop

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C++ does not require an implementation to use ASCII, although it does guarantee the range from `0` to `9` to be contiguous. – Christian Hackl Oct 10 '14 at 14:47
Thanx I just realised that what I wanted to do was not going to work anyway – Charl Meyers Oct 14 '14 at 16:30

Test converted int to char if it is number c++

3 Answers3

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