用有效数字位来比较浮点数
#include <stdio.h>
int main()
{
float b = 1.456;
if(b-1.456 > -0.000001 && b-1.456<0.000001)
printf("b is equal to 1.456\n");
else
printf("f is not equal to 1.456\n");
return 0;
}