#include <stdio.h>
#define PRE_LOOP  123
#define PRE_LOOP22  1020
#define PRINT_LOOP 58
// PRE_LOOP22 : used  for double
int main( ) {
    float a, b;  int i;
    double x, y;

  /**Underflow (虧失) 絕對值太小小到幾乎是 0 以致於被電腦當作 0:
             整數不會 Underflow, 因為 1 再小就變 0;
             實數才會:***/

      printf("a, b are float.\n");
            a = 1.0, b= 1.0;
            for(i=1; i<= PRE_LOOP; ++i) {
                 a = a*2;
                 b = b / 2;
            }
          printf("a=%.8f, b=%.8f\n", a, b);  // %f
            for(i=1; i<= PRINT_LOOP; ++i) {
                 a = a*2;   // 會 overflow
                 b = b / 2;   // 會 underflow
                 printf("a=%.8g, b=%.8g\n", a, b);
            }
///
      printf("\nx, y are double.\n");
      x = y = 1.0;
            for(i=1; i<= PRE_LOOP22; ++i) {
                 x = x*2;
                 y = y / 2;
            }
           printf("x=%.18f, y=%.18f\n", x, y);   // %f
            for(i=1; i<= PRINT_LOOP; ++i) {
                 x = x*2;   // 會 overflow
                 y = y / 2;   // 會 underflow
                 printf("x=%.18g, y=%.18g\n", x, y);
            }
}