C code : Check whether alphanumeric value falls in specific alphanumeric range

Question

How can I check with a C code, whether a given string falls within the start and stop range of alphanumeric values?

Eg : 
given_string = "G32"
start_string = "F00"
stop_string  = "H44"

The valid sequence here will be a set of values below:
F00 F01 F02 ------ F99
G00 G01 G02 G03 ----- G99
H00 H01 H02 H03 ----- H44

So in this case G32 falls in the range F00 - H44. Hence G32 will be valid. If we consider E99 or H45, they will not fall in the range. Hence they will be invalid.

Answer 1

Something like this should work:

#include <stdio.h>
#include <ctype.h>

typedef struct {
    char letter;
    int number;
} value_t;

value_t get_value(char *str)
{
    value_t result;

    if (strlen(str) != 3  ||    // Validate that string is 3 characters long
            !isupper(*str)  ||  // Validate that first character is uppercase
            !isdigit(str[1]  ||  !isdigit(str[2])) {  // Validate that remaining characters are digits
        printf("Invalid string!\n");
        exit(-1);
    }
    result.letter = *str;
    result.number = (str[1] - '0') * 10 + (str[2] - '0');
    return result;
}

int in_range(value_t min,value_t max,value_t val)
{
    if (val.letter < min.letter  ||  (val.letter == min.letter  &&  val.number < min.number))
        return 0;
    if (val.letter > max.letter  ||  (val.letter == max.letter  &&  val.number > max.number))
        return 0;
    return 1;
}

int main(int argc,char *argv[])
{
    value_t MIN = { 'F', 0 }, MAX = { 'H', 44 }, val;

    val = get_value(argv[1]);
    if (in_range(MIN,MAX,val))
        printf("%s is in range\n",argv[1]);
    else
        printf("%s is out of range\n",argv[1]);
}