关系运算符的链接给出了错误的输出

Question

谁能给我解释一下？我做错什么了吗？当我运行程序时，它没有显示正确答案。

例如：当我输入体重 = 50 公斤和身高 = 130 厘米时，答案应该是

"Your BMI is 29.58. You are overweight2.You will have a chance to cause high blood pressure and diabetes need to control diet. And fitness."

但显示的答案是

"Your BMI is 29.58. You are normal......"

#include<stdio.h>
#include<conio.h>

int main() {
  float weight, height, bmi;

  printf("\nWelcome to program");

  printf("\nPlease enter your weight(kg) :");
  scanf("%f", &weight);

  printf("\nPlease enter your height(cm) :");
  scanf("%f", &height);

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

  if(bmi<18.50) { 
    printf("Your bmi is : %.2f",bmi);
    printf("You are Underweight.You should eat quality food and a sufficient amount of energy and exercise proper.");
  } else if(18.5<=bmi<23) {
    printf("Your bmi is : %.2f \nYou are normal.You should eat quality food and exercise proper.",bmi);
  } else if(23<=bmi<25) {
    printf("Your bmi is : %.2f \nYou are overweight1 if you have diabetes or high cholesterol,You should lose weight body mass index less than 23. ",bmi);
  } else if(25<=bmi<30) {
    printf("Your bmi is : %.2f \nYou are overweight2.You will have a chance to cause high blood pressure and diabetes need to control diet. And fitness.",bmi);
  } else if(bmi>=30) {
    printf("Your bmi is : %.2f \nYou are Obesity.Your risk of diseases that accompany obesity.you run the risk of highly pathogenic. You have to control food And serious fitness.",bmi);
  } else {
    printf(" Please try again! ");
  }

  return 0;
  getch();
}

Answer 1

在您的代码中，您已经尝试过

 else if(18.5<=bmi<23)

不，这种关系运算符的链接在C中是不可能的。你应该写

 else if((18.5<=bmi) &&  (bmi < 23))

检查 [18.5, 23) 中的 bmi 值，其他情况依此类推。

编辑：

只是为了详细说明问题，像

这样的表达

18.5<=bmi<23

是完全有效的 C 语法。不过本质上和

是一样的

((18.5<=bmi) < 23 )

由于 operator associativity.

因此，首先对 (18.5<=bmi) 求值，然后将结果（0 或 1）与 23 比较，这当然不是您想要的。

Answer 2

这个：

18.5<=bmi<23

与

的含义相同

(18.5 <= bmi) < 23

换句话说，bmi 的值永远不会与 23 进行比较。在C里一定不能用那种math-syntax，应该写成：

(18.5 <= bmi) && (bmi < 23)

所以它实际上是两次变量的比较，并且必须使用boolean-and（&&）运算符来编写以使其显式。

Answer 3

是的，C 语言确实向您展示了您所尝试的正确答案。

C 中没有这样的语法用于比较（但是是的，这是一个有效的语法）：

else if(18.5<=bmi<23)

应该是这样的：

else if((18.5<=bmi)&&(bmi < 23))

关系运算符的链接给出了错误的输出

Chaining of Relational operators is giving wrong output

c

operators

comparison-operators