c - Function returns only letters of string -

i wrote program should take string , return string letters original one, it's not working , can't figure out why. can me?

#include<stdio.h>  char *only_letters(char *s1ptr, char *s2ptr) {     while(*s1ptr)     {         if((*s1ptr >= 'a' && *s1ptr <= 'z') || (*s1ptr >= 'a' && *s1ptr <= 'z'))         {             *s2ptr = *s1ptr;             s2ptr++;         }         s1ptr++;     }     *s2ptr = '\0';     return s2ptr; }  int main() {     char *s1ptr, *s2ptr;     printf("\n write string:\n");     scanf("%s", s1ptr);     printf("\n%s\n", *only_letters(s1ptr, s2ptr));     return 0; } 

you have 3 problems.

1. s1ptr , s2ptr 2 unallocated arrays caused undefined behavior.

2. you're incrementing s2ptr point has value \0. after returning have string has \0.

3. to show string, must pass without * (don't dereference it).

try this

char *only_letters(char *s1ptr, char *s2ptr_) {     char *s2ptr = s2ptr_;     while(*s1ptr)     {         if((*s1ptr >= 'a' && *s1ptr <= 'z') || (*s1ptr >= 'a' && *s1ptr <= 'z'))         {             *s2ptr = *s1ptr;             s2ptr++;         }         s1ptr++;     }     *s2ptr = '\0';      return s2ptr_; }  int main() {     char s1ptr[256]; // long enough     char s2ptr[256]; // long enough     printf("\n write string:\n");     scanf("%s", s1ptr);     printf("\n%s\n", only_letters(s1ptr, s2ptr)); }