问题
Can anyone explain this to me? Did I do something wrong? When I run the program it doesn't show me the right answer.
ex : when I type weight = 50 kg and height = 130 cm the answer should be
"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."
but the answer that shows is
"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();
}
回答1:
In your code, what you've tried
else if(18.5<=bmi<23)
No, this kind of chaining of Relational operators is not possible in C. You should write
else if((18.5<=bmi) && (bmi < 23))
to check bmi value in [18.5, 23) and so on for the other cases.
EDIT:
Just to elaborate about the issue, an expression like
18.5<=bmi<23
is perfectly valid C syntax. However, it is essentially the same as
((18.5<=bmi) < 23 )
due to the operator associativity.
So, first the (18.5<=bmi) is evaluated and the result , (0 or 1) gets to get comapred against 23, which is certainly not you want here.
回答2:
This:
18.5<=bmi<23
means the same as
(18.5 <= bmi) < 23
In other words the value of bmi is never compared to 23. You must not use that kind of math-syntax in C, it should be written as:
(18.5 <= bmi) && (bmi < 23)
So it's really two comparisons of the variable, and must be written using the boolean-and (&&) operator to make this explicit.
回答3:
Yes, C language does show you the right answer of what you've tried.
There is no syntax like this in C for comparison (but yes, it's a valid syntax):
else if(18.5<=bmi<23)
it should be this:
else if((18.5<=bmi)&&(bmi < 23))
来源：https://stackoverflow.com/questions/35059133/chaining-of-relational-operators-is-giving-wrong-output