c++对类构造函数的未定义引用

//Header FILE:
#ifndef BMI_H_INCLUDED
#define BMI_H_INCLUDED
#include<iostream>
#include<string>
using namespace std;
class BMI{
public:
//default constructer
BMI();
//overloaded
BMI(string,int,double);
private:
string newName;
int newHeight;
double newWeight;
};

#endif // BMI_H_INCLUDED
//Implementation file:
#include "BMI.h"
BMI ::BMI(){
newHeight=0;
newWeight=0.0;
}
BMI::BMI(string name,intheight,double weight){
newName=name;
newHeight=height;
newWeight=weight;
}
//Main file:
#include <iostream>
#include<string>
#include "BMI.h"
using namespace std;
int main()
{
string name;
int height;
double weight;
cout<<"Name:n";
getline(cin,name);
cout<<"Height(Inches):n";
cin>>height;
cout<<"Weight(Pounds):";
cin>>weight;
BMI person_1("John",89,90.0);
//I get the error on the above line error is             //undefinedreferenceto`BMI::BMI(std::string, int, double)'

}

有人知道为什么这种事一直发生在我身上吗？

我使用代码块，如果是这样，我该如何修复并防止它再次发生。

每当我将类分离为头文件和cpp文件时，就会发生这种情况。这只是我的程序因此而多次编译失败的一次。