ASCII to hex

Alsalamo Alaykom whoever following me :)

Today I am coming for you with a complete app in C, it is simple but yet complete and do a great job.

For some reason I wanted to convert from ASCII to hex, I know that many Linux app already exist for that (oc, hexdump), but may be I found them hard to use correctly :)

The following is a simple but complete app you can use for that purpose, have fun :) :

/*
 * @auther mhewedy
 * @email mohammed_a_hewedy@hotmail.com
 * @tested under gcc (GCC) 3.4.2 (mingw-special) (quite old :) )
 */

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

char* usage(char*);

int main(int argc, char* argv[])
{
    if (argc <= 1)
    {
        char* usage_string = usage(argv[0]);
        printf("%s\n", usage_string);
        free(usage_string);
        exit(1);
    }

    int s_option_present =0;
    char* string = NULL;

    if (strcmp("-s", argv[1]) != 0)
        string = argv[1];
    else
    {
        string = argv[2];
        s_option_present = 1;
    }

    while (*string != '\0')
    {
        printf("%X%s", *string++, (s_option_present? " " : ""));
    }
    printf("\n");

    return 0;
}

char* usage(char* app_name)
{
    char* usage = (char*) calloc(40, sizeof(char*));
    strcpy(usage, "Usage: ");
    strcat(usage, app_name);
    strcat(usage, " [-s] {ascii string}");
    return usage;
}

Example of usage:
atohex.exe -s ABC
atohex.exe -s 1
atohex.exe hello