函数中未初始化的局部变量

Question

我试图模块化我以前工作过的程序。我已经把所有的东西都拿出来放到了函数中。我的问题是，当我拥有Main中的所有内容时，它工作良好，无需初始化变量并等待用户输入数字。现在，他们在函数中，我不断收到错误，他们没有初始化。为什么是这样？如果我让他们都0，那么当用户输入他们的人数变量留0。这里是我的代码：

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

void displayMenu(); 
void findSquareArea(); 
void findCircleArea(); 
void findTriangleArea(); 

const double PI = 3.14159; 

int main() 
{ 

displayMenu(); 

return 0; 
} 

void displayMenu() { 

int choice; 

do { 
    cout << "Make a selection for the shape you want to find the area of: \n"; 
    cout << "1. Square\n"; 
    cout << "2. Circle\n"; 
    cout << "3. Right Triangle\n"; 
    cout << "4. Quit\n"; 

    cin >> choice; 


    switch (choice) { 
    case 1: 
     findSquareArea(); 
     break; 

    case 2: 
     findCircleArea(); 
     break; 

    case 3: 
     findTriangleArea(); 
     break; 

    case 4: 
     exit(EXIT_FAILURE); 

    default: 
     cout << "Invalid entry, please run program again."; 
     break; 

    } 

    for (int i = 0; i <= 4; i++) { 
     cout << "\n"; 
    } 
} while (choice != 4); 

} 

void findSquareArea() { 

double length, 
    area = length * length; 

cout << "Enter the length of the square."; 
cin >> length; 
cout << "The area of your square is " << area << endl; 

} 

void findCircleArea() { 

double radius, 
    area = PI * (radius * radius); 

cout << "Enter the radius of the circle.\n"; 
cin >> radius; 
cout << "The area of your circle is " << area << endl; 

} 

void findTriangleArea() { 

double height, base, 
    area = (.5) * (base) * (height); 

cout << "Enter the height of the triangle.\n"; 
cin >> height; 
cout << "Enter the length of the base.\n"; 
cin >> base; 
cout << "The area of your triangle is " << area << endl; 

} 

Answer 1

您有基于未初始化的变量表达式，如area = length * length in double length, area = length * length;请注意，C++不像例如Excel，您可以在其中定义一个公式，该公式在参数更改时会自动重新计算。 “公式”在代码被陈述的地方进行评估。

所以你的代码像...

double length, 
    area = length * length; 

cout << "Enter the length of the square."; 
cin >> length; 
cout << "The area of your square is " << area << endl; 

应该这样写......

double length = 0.0, area; 


cout << "Enter the length of the square."; 
cin >> length; 
area = length * length; 
cout << "The area of your square is " << area << endl;