#include <stdio.h>
#include <string.h>

//Some said don't use strcpy() but use strncpy()!!!
int main () {
   char str1[128];
   char str2[256];
   int len1, len2;
//   strcpy(str1, "this is string1");
//   strcpy(str2, "That is test string2");
   len1=strlen("this is string1");
   len2=strlen("That is test string2");

   //memset(str1, '\0', sizeof(str1));   //why is it needed?
   strncpy(str1, "this is string1", len1);
   strncpy(str2, "That is test string2", len2);
   puts("___Line 1___");
   puts(str1);
   puts("___Line 2___");
   puts(str2);
   return (0);
}

this is string10That is test string2
That is test string2.

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

//Tried from scratch combining const/strlen/malloc/'\0' concepts

void swap(char* s1, char* s2) {
         *s1 = *s1 ^ *s2;
         *s2 = *s2 ^ *s1;
         *s1 = *s2 ^ *s1;
}

char* str_reverse_in_place_by_swap(char* str){
    int len = strlen(str);
    char* start = str;
    char* end = start + len - 1; //-1 for '\0'; Made a mistake: char* end = start + len 
;
    while(start < end )
    {
        swap(start, end);
        ++start;
        --end;
    }
return str;
}


int main(int argc, char *argv[])
{
  char* string1 = malloc(256*sizeof(char));    //first allocate 256 bytes long

  printf("Type a String to reverse it[max. 255 chars]:\n");

  if (fgets(string1, 256, stdin) == NULL)
      printf("Error! Non-empty string is needed!\n");

  char* str3 = malloc( (strlen(string1)+1) * sizeof(char) );
  printf("Before reverse string1(which should be empty!): %s\n", str3);

  printf("By reverse_in_place_by_swap():");
//  str3 = str_reverse_in_place_by_swap(string1);
//  puts(str_reverse_in_place_by_swap(string1));
  printf("%s\n", str_reverse_in_place_by_swap(string1));
  free(str3);

  return EXIT_SUCCESS;
}