ASCII to decimal value

The characters that represent decimal digits are laid out in ASCII space in numerical order.

• '0' is ASCII 0x30
• '1' is ASCII 0x31
• '2' is ASCII 0x32
• and so on.

This means that you can simply subtract '0' from your character to get the value you desire.

char a = ...;
if (a >= '0' && a <= '9')
{
    int digit = a - '0';
    // do something with digit
}

USe

char a = '4';     //ASCII value of '4' is 52
int b = a - '0';  // ASCii value of '0' is 48 so 52-48 will return 4.
printf("%d", b);  //It will print 4.

• ASCII value of 0 [in hex] == 30.
• ASCII value of 9 [in hex] == 39.

Hope you got the relation. To get the character value as integer, just subtract the ASCII value of 0 from the char variable itself. The difference will be same as the value.

For details, check the ASCII table here.

As example,

char cInput = `4`;
int iInput;

iInput = cInput - `0`;

printf("as integer = %d\n", iInput);

Will print 4.

ASCII conversion to value for characters in ranges a-f, A-F, or 0-9 can be accomplished with a switch statement, as is used in the following function:

unsigned char convert(unsigned char ch) {
    unsigned char value;
    switch (ch) {
        case 'A' :
        case 'B':
        case 'C':
        case 'D':
        case 'E':
        case 'F': value = ch + 10 - 'A';  break;
        case 'a':
        case 'b':
        case 'c':
        case 'd':
        case 'e':
        case 'f': value = ch + 10 - 'a';  break;
        default: value = ch - '0';
    }
    return value;
}

Some clarifications about your statement

This gives the hex value of '4'

by doing:

char a  = '4';

you put the ASCII value of '4' - which maps to 0x34, in to the one byte variable 'a'.

The action:

int c = (int) a; 

is called casting. what it does is copying the value inside 'a' (one byte) into the value in 'c' (4 bytes). Therefore, the value inside 'c' would be 0x00000034 (the other 3 bytes are initialized to zero).

Finally, when you want to print the value, you could do it in any way you want. printf("%d",c); will give you the decimal value - 52, whereas printf("%x",c); will give you the hexadecimal value.

Cheers,

#include <string.h>

#include void main(){ if(!strcmp(name,"Jan") printf("wellcom Jan"); else printf("Error"); }