Geek Answers Handbook

Please explain what this code does (someChar-48)

I am experiencing some practice problems, and I saw this code:

#include <stdio.h> #include <string.h> int main(void) { char* s = "357"; int sum = 0; int i = 0; for (i = 0; i < strlen(s); i++) { sum += s[i] - 48; } printf("Sum is %d", sum); return 0; }

Can someone explain what the code does, especially the 48-part subtraction?

+6
c char encoding ascii
source share
4 answers

The code basically summarizes the digits of a number represented as a string. This makes two important assumptions for proper operation:

  • The string contains only characters in the range '0'..'9'
  • Used character encoding - ASCII

In ASCII, '0' == 48 , '1' == 49 , etc. Thus, '0' - 48 == 0 , '1' - 48 == 1 , etc. That is, subtraction by 48 converts the char values '0'..'9' into int values 0..9 .

Thus, precisely because '0' == 48 , the code will also work with:

 sum += s[i] - '0';

In this version, maybe a little more clearly.

You can, of course, do a “reverse” mapping by adding, for example. 5 + '0' == '5' . Similarly, if you have a char containing a letter in the range 'A'..'Z' , you can subtract 'A' from it to get the index of that letter in the range 0..25 .

see also

Related Questions

  • How to convert one char to int
  • Mapping languages: convert a string of numbers to an array of integers?
    • Many examples of converting these numbers using subtraction using '0' and 48 !

About alternative encodings

As already mentioned, the source code - 48 assumes that the character encoding used is ASCII. - '0' not only improves readability, but also abandons the assumption of ASCII and will work with any encoding, as indicated by the C language, which provides that digital characters must be encoded sequentially in a continuous block.

On the other hand, letters are not being made. Thus, in a rare situation when you use EBCDIC encoding, for example, matching 'A'..'Z' - 0..25 is not as simple as subtracting 'A' , because the letters are NOT encoded sequentially in a continuous block in EBCDIC.

Some programming languages ​​simplify issues by indicating that one particular encoding is used to represent the source code (for example, Java uses Unicode: JLS §3.1 )

see also

Related Questions

  • Are the numbers represented in sequence in all text encodings?
+29
source share

Search for the sum of numbers in string s.

sum += s[i] - 48; converts ASCII characters to their numeric values.

+5
source share

its addition 3 + 5 + 7 and then printing

Amount is 15

The -48 part is that it subtracts the character 0, i.e. the ascii value for 0.

So what he does is

 '3' - '0' > 51 - 48 '5' - '0' > 53 - 48 '7' - '0' > 55 - 48

As you can see, in C, '0' (the character zero) is different from 0 (the number 0). They have different meanings (among other things)

+2
source share

I suggest writing a test program to see s [] being displayed. You can also print all the values ​​for each entry in "0123456789".

I think you will quickly understand what it does, although this code relies on ASCII encoding.

Good luck

+1
source share

More articles:


All Articles