c++ - 在 C++ 上编译错误，未在此范围内声明 calcarea

Question

我正在学习 C++，并且正在做这个使用函数打印三角形面积的练习，但是当我尝试编译时出现错误“[Error] 'calcarea' was not declared in this scope”

#include<iostream>
#include<cstdlib>
using namespace std;
double farea;

main(){
    float base, height;
    cout<<"Enter base of triangle: ";   cin>>base;
    cout<<"Enter height of triangle: "; cin>>height;
    cout<<endl;

    farea = calcarea(base,height);
    cout<<"The area of the triangle is: "<<farea;
    system("pause>nul");
}

double calcarea(float ba, float he){
    double area;

    area = (ba*he)/2;
    return area;
}

Answer 1

您的编译器从头到尾读取代码，当它第一次遇到一个符号时，在本例中为 calcarea，它会检查该符号是否已声明。由于 calcarea 仅在 之后声明，编译器当时并不知道此符号，因此，它是错误的:calcarea 未在此范围内声明

如果您将函数移动到它第一次调用之前，这个错误将得到解决。解决这个问题的另一种方法是只在 main 之前声明函数，然后在 main 之后定义它，这意味着，你将把你的函数留在原处，但在 main 之前添加一行定义它:double calcarea(float ba , float 他);

main(){
    float base, height;
    cout<<"Enter base of triangle: ";   cin>>base;
    cout<<"Enter height of triangle: "; cin>>height;
    cout<<endl;

    farea = calcarea(base,height); // here your compiler must already know what is calcarea, either by moving the definition, or only adding declaration 
    cout<<"The area of the triangle is: "<<farea;
    system("pause>nul");
}