text: // ex9: while loop
  
  #include <stdio.h>
  
  int main(int argc, char *argv[])
  {
    int i = 0; // if not initiate i, will get warning: variable 'i' is uninitialized when used here
    // but most of the version of C on most of the platform, it will auto initialized with 0,
    // but do not count on this, alway initialize an variable
  
    // this while loop just print out 0 to 24
    while (i < 25) {
      printf("%d\n", i);
      i++;
    }
  
    int j = 25;
    // this print out from 25 to 0
    while(j >= 0) {
      printf("%d\n", j);
      j--;
    }
  
    return 0;
  }
  