Thread: String to Numeric Value

I am looking to convert a string (e.g. "F8A2" or "-927") into its numeric value. I figure I need to do it one char at a time but how does "A" become "10" and "9" become the value 9. I need to do math on these characters so they need to become numbers. Is there a function for this or do I need to create a huge switch loop that sets each valid decimal or hexadecimal character into another int variable.

Thanks in advance.

Yah I've been looking at the ASCII table but "2" + "7" should equal 9 not 105 (50 + 55). I need "B" to equal 11 and "F" to equal 15, etc. Create my own lookup in the c program???

That looks like hex (hexadecimal) to me:

0-F: 0123456789ABCDEF

This is base 16, so numbers in it are valued 0 through 15, for each of them. The letters are just larger numbers here. Don't think of them as letters with hex.

Thanks for all your help people. I ended up just creating a function that accepts a char and returns an int. Switch statement with every option for 0-9 and AaBbCcDdEeFf. Pain in the ass but I guess C doesn't have a built in function. Strtol() maybe does the job but didn't try it. I love C...its like going to the dentist. =)

Originally Posted by rwagstaff

Thanks for all your help people. I ended up just creating a function that accepts a char and returns an int. Switch statement with every option for 0-9 and AaBbCcDdEeFf. Pain in the ass but I guess C doesn't have a built in function. Strtol() maybe does the job but didn't try it. I love C...its like going to the dentist. =)

I'm just amazed you didn't use a hex printf() format when you needed to, and a decimal format, whenever you needed to.

Code:

#include <stdio.h>

int main (void) {

   int i=152;

   printf("i in hex: %x   i in decimal: %d\n",i, i); //use %X for cap letters in hex

   return 0;
}

Maybe I didn't understand your problem, however.

Well I am just a noob trying to learn how to program. I appreciate your help everyone. Please review the function below and discuss my ineptness. Thanks a bunch!! =)

Code:

int HexValue(char c)
{
    switch(c)
    {
        case 'A':
            return 10;
            break;
        case 'a':
            return 10;
            break;
        case 'B':
            return 11;
            break;
        case 'b':
            return 11;
            break;
        case 'C':
            return 12;
            break;
        case 'c':
            return 12;
            break;
        case 'D':
            return 13;
            break;
        case 'd':
            return 13;
            break;
        case 'E':
            return 14;
            break;
        case 'e':
            return 14;
            break;
        case 'F':
            return 15;
            break;
        case 'f':
            return 15;
            break;
        case '0':
            return 0;
            break;
        case '1':
            return 1;
            break;
        case '2':
            return 2;
            break;
        case '3':
            return 3;
            break;
        case '4':
            return 4;
            break;
        case '5':
            return 5;
            break;
        case '6':
            return 6;
            break;
        case '7':
            return 7;
            break;
        case '8':
            return 8;
            break;
        case '9':
            return 9;
            break;
        default :
            return 0;
    }
}

And here would be the calling statement which would result in num being equal to 27. (15 + 12)

Code:

int num;
num = HexValue("F") + HexValue("C");

Why does it number the code with strange numbers and put a huge amount of blank white space at the bottom when I submit code blocks???? Anyone??? I'm a newbie. =)

Originally Posted by rwagstaff

Why does it number the code with strange numbers and put a huge amount of blank white space at the bottom when I submit code blocks???? Anyone??? I'm a newbie. =)

I'm floored that you don't want to use the hex format C has built into printf() for you. Why?

"F" is a string with two char's - an 'F' char (note the single quotation mark on each side, not a double), and an end of string char: '\0'.

Use a char, not a string, to compare to a char in your switch test.