CODEWITHSUNDEEP
ctype-conversionintegercharacter
Goose9192
Goose9192

Reputation: 107

Issue with turning a character into an integer in C

I am having issues with converting character variables into integer variables. This is my code:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>


int main()
{
    char string[] = "A2";
    char letter = string[0];
    char number = string[1];
    char numbers[] = "12345678";
    char letters[] = "ABCDEFGH";
    int row;
    int column;

    for(int i = 0; i < 8; i++){
        if(number == numbers[i]){
            row = number;
        }
    }
}

When I try to convert the variable row into the integer value of the variable number, instead of 2 I get 50. The goal so far is to convert the variable row into the accurate value of the character variable number, which in this case is 2. I'm a little confused as to why the variable row is 50 and not 2. Can any one explain to me why it is not converting accurately?

Upvotes: 4

Views: 87

Answers (2)

erik258
erik258

Reputation: 16304

2 in your case is a character, and that character's value is 50 because that's the decimal version of the byte value that represents the character 2 in ASCII. Remember, c is very low level and characters are essentially the same thing as any other value: a sequence of bytes. Just like letters are represented as bytes, so are the character representation of their value in our base 10 system. It might seem that 2 should have been represented with the value 2, but it wasn't.

If you use the atoi function, it will look at the string and compute the decimal value represented by the characters in your string.

However, if you're only converting one character to the decimal value it represents , you can take a short cut. subtract the digit from the value of '0'. Though the digits are not represented by the base 10 value they have for us humans, they are ordered sequentially in the ASCII code. And since in C the characters are simply byte values, the difference between a numeric character 0-9 and 0 is the value of the character.

char c = '2'; 
int i = c - '0';

If you understand why that would work, you get what I'm saying.

Upvotes: 2

nemequ
nemequ

Reputation: 17482

'2' != 2. The '2' character, in ASCII, is 50 in decimal (0x32 in hex). See http://www.asciitable.com/

If you're sure they're really numbers you can just use (numbers[i] - '0') to get the value you're looking for.

Upvotes: 4

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