How is each character group in the control string identified in c code example

Example: string in c

#include <stdio.h>

int main() {
  char *str1 = strdup("Hello");
  char *str2 = malloc(sizeof(char) * (strlen(str1) + 1));
  
  for (int i = 0; i < strlen(str1); ++i)
    str2[i] = str1[i];
  str2[strlen(str1)] = '\0'; // very important, the string stop to print
  printf("%s --> %s\n", str1, str2);
}