第20页

科学计数法
Floating-point arithmetic is not associative due to the finite precision of the representation. 
 浮点运算是不可结合的

不能组合的，不能组合运算的。没有结合律的?

在printf代码里面直接写200*300*400*500, gcc会提示warning
  printf("200*300*400*500 = %i \n", 200*300*400*500);

 integer overflow in expression [-Woverflow]

/* $begin hello */
#include <stdio.h>

int main() 
{
  printf("3.14+1e20 = %f \n", 3.14+1e20-1e20);
  printf("3.14 + 1e20 - 1e20 = %f \n", 3.14+1e20-1e20);
  printf("3.14 + (1e20 - 1e20) =  %f \n", 3.14+(1e20-1e20));
  printf("200*300*400*500 = %i \n", 200*300*400*500);
  /*  printf("hello, world\n"); */
}
/* $end hello */



3.14+1e20 = 0.000000 
3.14 + 1e20 - 1e20 = 0.000000 
3.14 + (1e20 - 1e20) =  3.140000 
200*300*400*500 = -884901888