/*Calculator to escape for check sum error*/

#include <stdio.h>

#define MAX 10                  //Maximum string length
#define MAX_HEX 4               //Maximum output heximal

void hex(int);
void usage(void);


int main()
{
        char ch[MAX+1];
        int i;                  //roof counter
        int num;
        char* endptr;

        while(1)
        {
                //buffer clear
                __fpurge(stdin);

                printf("Enter decimal:");

                fgets(ch, MAX+1, stdin);

                for(i=0; i<=MAX; i++)
                {
                        /*change '\n' to '\0'*/
                        if(ch[i]=='\n')
                        {
                                ch[i] = '\0';
                                break;
                        }
                }

                if(strcmp(ch, "quit")==0)
                        break;
                else if(strcmp(ch, "q")==0)
                        break;
                /*change String to integer*/
                num=strtol(ch, &endptr, 10);

                if(num > 65535 || num <0)
                {
                        usage();
                        continue;
                }
                if(*endptr != '\0')
                {
                        /*Chek the decimal input*/
                        usage();
                        continue;
                }

                /*Change to Hex*/
                hex(num);

        }

        return 0;
}

/*change the decimal number to heximal number*/
void hex(int num)
{
        //Charactor array for Presentation heximal
        char code[16] = {'0','1','2','3','4','5','6','7','8','9',
                                        'A','B','C','D','E','F'};
        //Array for heximal code
        char str[MAX_HEX];
        int i;

        //Initialize code Array
        for(i = 0; i < MAX_HEX; i++)
                str[i] = '0';

        printf("---------------The result---------------\n");
        printf("%d's value is...\n\n", num);
        //Convert decimal to heximal
        if(num<16)
        {
                str[0]=code[num];
        }
        else
        {
                for(i = 0; num >= 16; i++)
                {
                        str[i] = code[num%16];
                        num = num/16;
                        if(num<16)
                        {
                                str[i+1]=code[num];
                                break;
                        }
                }
        }

        //output of Array by big endian sequencing
        printf("Heximal data by big endian\n");
        for(i=MAX_HEX-1; i>=0; i-=2)
        {
                printf("%c%c ",str[i],str[i-1]);
        }
        printf("\n\n");
        //output of Array by little endian sequencing
        printf("Converting heximal to little endian\n");
        for(i=0; i<MAX_HEX; i+=2)
        {
                printf("%c%c ",str[i+1],str[i]);
        }
        printf("\n----------------------------------------\n\n");

}

void usage()
{
        printf("Please Input correct Decimal integer.\n");
        printf("Input range is from 0 to 65535\n");
        printf("If you want to close this program ");
        printf("input \"quit\"or \"q\".\n");
}