BMI计算器C $ C $Ç [英] BMI calculator C code

问题描述

我试图写一个简单的BMI计算器，但由于某些原因，当我尝试175高度（其配方使1.75）和70大众应该给予22.8，这是在正常范围内，但它给我减持。我知道这可能是一个简单的错误，但我不能看到它。

 浮动主要（无效）{    浮动高度;
    的printf（中输入厘米你的身高：\\ n）;
    scanf函数（％F，＆安培;高度）;    浮重;
    的printf（公斤输入您的体重：\\ n）;
    scanf函数（％F，＆安培;重量）;    浮BMI;
    BMI =（重量/（身高/ 100）*（高度/ 100））;    如果（BMI＆LT; = 16）{
        的printf（体重严重不足\\ n）;
    }
    否则，如果（16＆LT; BMI＆LT; = 18.5）{
        的printf（减持\\ n）;
    }
    否则，如果（18.5＆LT; BMI＆LT; = 25）{
        的printf（健康\\ n）;
    }
    否则如果（25℃; BMI＆下; = 30）{
        的printf（增持\\ n）;
    }
    其他{
        的printf（严重超重\\ n）;
    }
}
 

解决方案

所有这些

 否则如果（16＆LT; BMI＆LT; = 18.5）{
 

是错误的。他们不这样做，你的意思是他们做的事。以实现所期望的结果，可以使用

 否则如果（16＆LT; BMI＆放大器;＆安培; BMI＆LT; = 18.5）{
 

原因是，你的前pressions被评为

 否则如果（（16 LT; BMI）LT = 18.5）{
 

其中，（16＆LT; BMI）计算结果为真正或假这又等于 1 或 0 ，然后被相比，第二恒定。它之所以像这样评价，是因为比较运营商的左结合，因而是从左向右的。

编辑2

强制性SO链接：<一个href=\"http://stackoverflow.com/questions/8889522/is-4-y-1-a-valid-statement-in-c-how-do-you-evaluate-it-if-so\">Is （4> Y> 1）有效的在C ++中声明？你如何如果是这样评价它？

修改

我怀疑这一个，但不知道该公式。现在@MOehm已确认（和维基百科似乎证实了这一点为好）：

  BMI =（体重/（身高/ 100）*（高度/ 100））;
 

应成为

  BMI =（体重/（（身高/ 100）*（高度/ 100）））;
 

原因这里是pretty大同小异：运营商precedence和前$ P $用C pssion评价规则++。 OP，要注意这些方面，并把括号酌情！

修改3 这是我怎么会去这个使用STL（这种方法也有明显的前pressing算法背后的想法的利益，没有掩埋它的实现细节下面）：

 的#include＆LT;＆iostream的GT;
＃包括LT＆;串GT;
＃包括LT＆;矢量＆GT;
＃包括LT＆;实用＆GT;
＃包括LT＆;限制和GT;
＃包括LT＆;＆算法GT;诠释的main（）
{
    的std ::矢量＆lt;的std ::对＆LT;浮动，标准::字符串＆GT; ＆GT; bmi_table = {
        {16，严重不足}，
        {18.5，减持}，
        {25，健康}，
        {30，增持}，
        {的std :: numeric_limits＆LT;浮动＆GT; :: MAX（），严重超重}
    };
    浮身高，体重;
    给std :: cin＆GT;＆GT;高度＆GT;＆GT;重量;
    常量浮BMI =（重量/（（高度/ 100.f）*（高度/ 100.f）））;
    常量汽车IDX =
        的std :: find_if（bmi_table.begin（）
                     bmi_table.end（），
                     [＆放大器;（decltype（bmi_table）:: VALUE_TYPE＆安培; P） - ＆GT;布尔{返回p.first＆GT; BMI; }）;
    性病::法院LT＆;＆LT; idx-＆gt;第二个＆LT;＆LT;的'\\ n';
    返回0;
}
 

I'm trying to write a simple BMI calculator, but for some reason when I try 175 for height (which the formula makes 1.75) and 70 for mass it should give 22.8, which is in the healthy range, but it gives me underweight. I know it's probably a simple mistake, but I can't see it.

float main(void) { 

    float height;   
    printf("Enter your height in cm:\n");
    scanf("%f",&height);    

    float weight; 
    printf("Enter your weight in kg:\n");
    scanf("%f",&weight);

    float bmi;
    bmi = (weight/(height/100)*(height/100));

    if (bmi <= 16) {
        printf("Severely Underweight\n");
    }
    else if (16 < bmi <= 18.5) {
        printf("Underweight\n");
    }
    else if (18.5 < bmi <= 25) {
        printf("Healthy\n");
    }
    else if (25 < bmi <= 30) {
        printf("Overweight\n");
    }
    else {
        printf("Severely Overweight\n");
    }
}

解决方案

All of these

else if (16 < bmi <= 18.5) {

are wrong. They don't do what you mean them to do. To achieve the desired result, use

else if (16 < bmi && bmi <= 18.5) {

The reason is, your expressions are evaluated as

else if ((16 < bmi) <= 18.5) {

where (16 < bmi) evaluates to true or false which in turn equals 1 or 0, and is then compared to the second constant. Reason why it is evaluated like so, is because the comparison operators are left-associative, thus are evaluated left-to-right.

Edit 2

Obligatory SO link: Is (4 > y > 1) a valid statement in C++? How do you evaluate it if so?

Edit

I suspected this one, but didn't know the formula. Now @MOehm has confirmed it (and wikipedia seems to confirm this as well):

bmi = (weight/(height/100)*(height/100));

should become

bmi = (weight/((height/100)*(height/100)));

The reason here is pretty much the same: operator precedence and expression evaluation rules in C++. OP, pay attention to these aspects and put parentheses where appropriate!

Edit 3 Here's how I'd go about this using STL (this approach has the benefit of clearly expressing the idea behind the algorithm, without burying it beneath the implementations details):

#include <iostream>
#include <string>
#include <vector>
#include <utility>
#include <limits>
#include <algorithm>

int main()
{
    std::vector<std::pair<float, std::string> > bmi_table = {
        { 16, "Severely Underweight" },
        { 18.5, "Underweight" },
        { 25, "Healthy" },
        { 30, "Overweight" },
        { std::numeric_limits<float>::max(), "Severely Overweight" }
    };
    float height, weight;
    std::cin >>  height >> weight;
    const float bmi = (weight/((height/100.f)*(height/100.f)));
    const auto idx =
        std::find_if(bmi_table.begin(),
                     bmi_table.end(),
                     [&](decltype(bmi_table)::value_type& p) -> bool { return p.first > bmi; });
    std::cout << idx->second << '\n';
    return 0;
}

这篇关于BMI计算器C $ C $Ç的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！