//以下是我打的代码，一般都是输入weight为80，height为2，得到结果为20，可是最后的判断结果总是Underweight: less than 18.5。
//用if{...}if{...}if{...}if{...}也是同样的判断结果。
//曾经尝试删去包含“Underweight: less than 18.5”的那个判断条件，最后直接得到结果20，没有其他判断结果。
//将整型int换成浮点型float也是出现同样的问题
#include <stdio.h>
#include <stdlib.h>
int main()
{
    int weight, height, BMI;//定义体重、身高
    int a = BMI = weight/(height*height);//定义身体质量指数BMI
    printf("Please enter weight(KG): ");
    scanf("%d", &weight);//输入体重
    printf("Please enter height(M): ");
    scanf("%d", &height);//输入身高
    printf("a = BMI = weight / (height * height) = %d\n", weight/(height*height));//得到结果
    if(a >= 18.5)
    {
        printf("Normal: between 18.5 and 24.9");
    }
    else if(a >= 25)
    {
        printf("Overweight: between 25 and 29.9");
    }
    else if(a >= 30)
    {
        printf("Obese: 30 or greater");
    }
    else
    {
        printf("Underweight: less than 18.5");
    }
    system("pause");
    return 0;
}

int a = BMI = weight/(height*height);//此处用到了除法操作，所以不能声明为整型，应该
声明为double类型，即可

你的a没有被赋值。

#include <stdio.h>
#include <stdlib.h>
int main()
{
    int weight, height, BMI;//定义体重、身高
    int a;
    printf("Please enter weight(KG): ");
    scanf("%d", &weight);//输入体重
    printf("Please enter height(M): ");
    scanf("%d", &height);//输入身高
    a = BMI = weight/(height*height);
    printf("a = BMI = weight / (height * height) = %d\n",a);//得到结果
    if(a >= 18.5)
    {
        printf("Normal: between 18.5 and 24.9");
    }
    else if(a >= 25)
    {
        printf("Overweight: between 25 and 29.9");
    }
    else if(a >= 30)
    {
        printf("Obese: 30 or greater");
    }
    else
    {
        printf("Underweight: less than 18.5");
    }
    system("pause");
    return 0;
}

这样改就行了，输入身高体重后面对a赋值。

[此贴子已经被作者于2019-2-9 01:29编辑过]

原来是这样，没试过double，是我疏忽了，谢谢了

是这样了，代码打得太乱，忘了检查赋值，谢谢了