浮点数与0比较

浮点数与0比较-CSDN博客

本来摘录自上面的文章,用以学习!感谢!

#include <QString>
#include <QDebug>
#include <stdio.h>
int main()
{
    double x=3.6;
    printf("%.50f\n",x);
    system("pause");
    return 0;
}

十进制转二进制时,有可能有精度损失.

不是一味的减少,也可能增多.

浮点数本身存储的时候,在计算不尽的时候,会"四舍五入"

#include<stdio.h>
#include <stdio.h>
#include <windows.h>
int main()
{
    double x = 1.0;
    double y = 0.1;
    printf("%.50f\n", x - 0.9);
    printf("%.50f\n", y);
    if ((x - 0.9) == y) {
        printf("you can see me!\n");
    }
    else {
        printf("oops\n");
    }
    system("pause");
    return 0;
}

有点看不懂啦!

#include <stdio.h>
#include <math.h>
#include <float.h>
#include <windows.h>
int main()
{
double x = 0.00000000000000000000001;
//if (fabs(x-0.0) < DBL_EPSILON){ //写法1
//if (fabs(x) < DBL_EPSILON){ //写法2
if(x > -DBL_EPSILON && x < DBL_EPSILON){ //书中写法
printf("you can see me!\n");
}
else{
printf("oops\n");
}
return 0;
}

/* The difference between 1 and the least value greater than 1 that is
   representable in the given floating point type, b**1-p.  */
#undef FLT_EPSILON
#undef DBL_EPSILON
#undef LDBL_EPSILON
#define FLT_EPSILON	__FLT_EPSILON__
#define DBL_EPSILON	__DBL_EPSILON__
#define LDBL_EPSILON	__LDBL_EPSILON__