C language traversal of the character array lookup method (custom header file)

Title: Find the first character in a string that appears only once. If you enter "Abaccdeff\0", Output ' B '. #ifndef  __select_first__#define __select_first__char select_first (char *p,int size); Char select_first1 (char *p, int size); Char select_first2 (char *p, int  size); #endif                                //header file    function declaration # include<stdio.h>//function Body #include<string.h>char select_first (char arr[],int size) {int  i = 0, j = 0;while  (Arr[i]) {if  ((arr[i] != arr[j]&& j< (size-1)) | | I==J) {j + +;} else{   j = 0;i++;} if  (j ==  (size - 1)) return arr[i];} return  ' + ';} Char select_first1 (char *p, int size) {char ch =  ' + '; char arr[20];int  i = 1,j=1;strcpy (arr,  p);while  (arr[0]) {ch = arr[0];i = 1; j = 1;while  (Arr[i]) { if  (Ch == arr[i]) {j + +;} Else{arr[i - j] = arr[i];} i++;} if  (j == 1) return ch;arr[i - j] =  ' \ n ';} return  ' + ';} Char select_first2 (char p[]) {int arr[255] = { 0 };char * ptr  = NULL;ptr = &p[0];while  (*p) {arr[*p]++;p + +;} while  (*ptr) {if  (arr[*ptr] == 1) return *ptr;ptr++;} return  ' + ';} #include <stdio.h>            //main function # include " Select_first.h "Int main () {char arr[] = " Abbaccdeff "; Char ch=select_first2 (Arr,strlen ( ARR));p rintf ("%c\n", ch);}

C language traversal of the character array lookup method (custom header file)