How to convert char to int in C/C++

I have encountered a problem when taking CS50’s Problem Set 1 where I need to convert a char number to int.

Luckily there is an easy and clever way to do that.

char_to_int function

int char_to_int(char character) {
  return character - '0';
}

The snippet above is a simple C/C++ function that takes char number and returns an int version of it.

So, how does it work?

Here is a part of the ASCII table.

Decimal	Character
48	0
49	1
50	2
51	3
52	4
53	5
54	6
55	7
56	8
57	9

See full ASCII table at: https://www.cs.cmu.edu/~pattis/15-1XX/common/handouts/ascii.html

It seems like each character has a decimal equivalent. If we use - on a char it uses the decimal equivalent to compute it.

So when we want to convert '8' to 8 and called char_to_int('8'), what actually happens to '8' - '0' is 56 - 48 which results into 8.

Another example would be '3' to 3 where it is interpreted as 51 - 48 which coincidentally equal to 3.

Note:

This only works with char and not string such as '14'.

That’s it for this topic. I hope you have a good use for it.