Aha! Algorithms (Column 2 of Programming Pearls)

 1 /* Copyright (C) 1999 Lucent Technologies */
 2 /* From 'Programming Pearls' by Jon Bentley */
 3 
 4 /* sign.c -- sign each line of a file for finding anagrams
 5     The input line "stop" gives the output line "opst stop"
 6  */
 7 
 8 #include <stdio.h>
 9 #include <stdlib.h>
10 #include <string.h>
11 #define WORDMAX 100
12 
13 int charcomp(char *x, char *y)
14 {   return *x - *y;
15 }
16 
17 int main()
18 {   char word[WORDMAX], sig[WORDMAX];
19     while (scanf("%s", word) != EOF) {
20         strcpy(sig, word);
21         qsort(sig, strlen(sig), sizeof(char), charcomp);
22         printf("%s %s\n", sig, word);
23     }
24     return 0;
25 }
26