[C language] Floating point number rounding

目录

一、Floating point numbers implement rounding

二、补充：ceil,floor,强制类型转换,round,Comparison of rounding methods and their application scenarios

一、Floating point numbers implement rounding

以保留3位数为例

1.直接实现【Do not use library functions】

int (x*1000+0.5)/1000.0;【特别注意,Here must be divided by yes1000.0】

2.间接实现【利用math函数库中的round】

二、补充：ceil,floor,强制类型转换,round,Comparison of rounding methods and their application scenarios

#include <stdio.h>
#include <math.h>
int main() 
{
    double x=3.863479, ret;
    //①ceil
    ret = ceil(x);
    printf("%lf\n", ret);
    //②floor
    ret = floor(x);
    printf("%lf\n", ret);
    //③强制类型转化——Implicit conversions are involved here
    ret = (int)x;
    printf("%.0lf\n", ret);
    //④round
    ret = round(x);
    printf("%lf\n", ret);
    //⑤四舍五入,比如说保留2位小数——两种实现方法
    //（1）round函数
    ret = round(x * 100) / 100.0;
    printf("%.2lf\n", ret);
    //（2）加减+强制类型转换
    ret =(int)(x*100+0.5) / 100.0;
    printf("%.2lf\n", ret);
    return 0;
}

Let's take a look at the running results~

 很显然,The following conclusions can be drawn

重要结论1

另外：这是cpluscplus对于ceil函数的解释,很容易看出,The return value and parameters are both floats,But its function is the largest integer greater than or equal to the current value

 同理,floor和round也是类似的

 重要结论2

 floorThe difference between functions and casts——The result obtained is an integer,The other is a floating point type

再叨叨几句：

1.ceilFind the largest integer that does not exceed the current value,返回值为浮点数

2.floorand mandatory typesintThe conversion evaluates to the largest integer not greater than the current value,The return value is a float and an integer

3.roundFind the closest integer value to the current value

4.There are casts and rounding of floating point numbersroundThere are two solutions to the function