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


// shows  stringcopy, stringcat and stringlength  FUNCTIONALITY

// we would need to #include <string.h> if we used
// strlen,   strcpy   and strcat instead of our own versions
// myStrlen, myStrcpy and myStrcat

// behaves just like strcpy in string library
char* myStrcpy(char* dest, char* src){
  char* dest0 = dest;
  while ( (*dest++ = *src++) != '\0');
  return dest0;
}

// behaves just like strcat in string library
char* myStrcat(char* dest, char* src){
  char* dest0 = dest;
  while (*dest != '\0') *dest++;  // WHY NOT: while(*dest++!='\0');  
  while ((*dest++ = *src++) != '\0');
  return dest0;
}

// behaves just like strlen in string library
int myStrlen(char* src){
  int len = 0;
  while (*src != '\0') {
    len++;
    *src++;
  }
  return len;
}

int main() {
  // a string
  char *hello = "hello";

  // a local array of chars 
  char localStr[30];

  // two dynamic array of chars

  // why do we need the +1?
  char *dynStr = malloc(myStrlen(hello)+1);
  char *catStr = malloc(30);

  // strcpy:  dest <- source
  myStrcpy(localStr, hello);
  printf("localStr after strcpy: %s, length: %d, NOT 30!\n", 
                                 localStr,   myStrlen(localStr));

  myStrcpy(dynStr, "goodbye, uhhh .... ");
  printf("dynStr after strcpy: %s\n", dynStr);

  // strcat concatenete dest after source
  // strcat: starts AT the '\0' delimter of dest and copies source there 
  myStrcat(dynStr, localStr);
  printf("dynStr after strcat: %s\n", dynStr);

}