Given a string, returns only the unique characters. i.e. abacb -> abc

uniqueChars.c

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

int in(char value, char* list){
  for (char *i = list; *i != '\0'; i++){
    if ( *i == value ){
      return 1;
    }
  }
  return 0;
}

char * uniqueChars(char *input) {
  char *result = calloc(100 ,sizeof(char*));
  char *p = result; // point to the beginning of the array for returning

  for( char *i = input; *i != '\0'; i++) {
    if ( in(*i, p) == 0) {
      // append i to result
      *result=*i;
      result++;
    }
  }
  return p;
}

int main(void) {
  char *one = "abc";
  char *two = "abca";
  char *three = "do androids dream of electric sheep?";

  printf("Testing %s\n", one);
  printf("%s\n", uniqueChars(one));
  printf("Testing %s\n", two);
  printf("%s\n", uniqueChars(two));
  printf("Testing %s\n", three);
  printf("%s\n", uniqueChars(three));
}

uniqueChars.py

#!/usr/bin/env python

def uniqueChars(input):
    result = ""
    for char in input:
        if not char in result:
            result += char
    return result

one = "abc"
two = "abca"
three = "do androids dream of electric sheep?"

print( uniqueChars(one))
print( uniqueChars(two))
print( uniqueChars(three))

uniqueChars.swift

#!/usr/bin/env xcrun swift

func uniqueChars(input: String) -> String{
    return reduce(input, ""){
        return $0 + ( contains($0,$1) ? "" : String($1) )
    }
}

let one = "abc"
let two = "abca"
let three = "do androids dream of electric sheep?"

println( uniqueChars(one) )
println( uniqueChars(two) )
println( uniqueChars(three) )