A String -> Hex -> Long -> Hex -> String Converter

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
unsigned char tmpByte[20];
char * hex2str(char *HEXStr) {
    int i, n;
    for (i = 0; i < strlen(HEXStr)/2; i++) {
        sscanf(HEXStr+2*i, "%2X", &n);
        tmpByte[i] = (char)n;
    }
    tmpByte[strlen(HEXStr)/2]=0;
    return tmpByte;
}
int back(long dec) {
    char hexstr[44];
    sprintf(hexstr, "%lx", dec);
    printf("%s\n",hexstr);
    printf("%s\n",hex2str(hexstr));
    return 0;
}

int main(void){
    char word[20], hexword[40];
    int i, len;
    long word_as_l;
    printf("Enter The words to convert:\n");
    fgets(word, sizeof(word), stdin);
    len = strlen(word);
    if (word[len-1]=='\n') word[--len] = '\0'; /*To be safe*/
    printf(" The length of the word is %i\n", len);
    for (i = 0; i<len; i++) {
        sprintf(hexword+i*2, "%02x", word[i]);
    }
    printf("%s\n", hexword);
    printf(" The length of the hexword is %i\n", strlen(hexword));
    word_as_l=strtol(hexword ,NULL, 16);
    printf(" The long\n%ld\n",word_as_l);
    printf("********Now Back********\n");
    back(word_as_l);
    return 0;
}

Three Runs:


[siegelj@tc-login bigInt]$ str2long2str
Enter The words to convert:
hello
 The length of the word is 5
68656c6c6f
 The length of the hexword is 10
 The long
448378203247
********Now Back********
68656c6c6f
hello

[siegelj@tc-login bigInt]$ str2long2str
Enter The words to convert:
good day
 The length of the word is 8
676f6f6420646179
 The length of the hexword is 16
 The long
7453298384152322425
********Now Back********
676f6f6420646179
good day
***********String is too long in the next run*************
[siegelj@tc-login bigInt]$ str2long2str
Enter The words to convert:
good week
 The length of the word is 9
676f6f64207765656b
 The length of the hexword is 18
 The long
9223372036854775807
********Now Back********
7fffffffffffffff
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[siegelj@tc-login bigInt]$