c++ - 我如何使用 main 函数和来自 getData 函数的用户输入将值初始化为 int 变量？

Question

In the main function, define four variables of type int, named: first, second, third, and total.

Write a function named getData that asks the user to input three integers and stores them in the variables first, second, and third which are in the main function.

Write a function named computeTotal that computes and returns the total of three integers.

Write a function named printAll that prints all the values in the format shown in the following sample:

1 + 2 + 3 = 6

Call the other three functions from the main function.

Test it once, with the values 4, 5, and 6.

#include <iostream>
using namespace std;

int getData() {
    cout << "Enter 3 Integer Values: ";
    cin >> first >> second >> third;
    return first, second, third;
}

int calcTotal() {
    total = first + second + third;
    return total;
}

int printTotal() {
    cout << total;
}

int main() {
    int first, second, third, total;
    getData();
    calcTotal();
    printTotal();
}

Answer 1

使用您描述的代码布局，这基本上是不可能的。

但是!

在 C++ 中可以使用称为传递引用的东西。默认情况下，当您将参数传递给函数时，值会被复制。但是按引用传递的作用是传递变量，而不是传递值。

例子:

#include <iostream>
void setToFive(int& x){// the ampersand signifies pass-by-reference
    x = 5; // This change is preserved outside of the function because x is pass-by-reference
}
int main(){
    int x = 200;
    std::cout << "X before = "<<x<<std::endl;
    setToFive(x);
    std::cout << "X after = "<<x<<std::endl;
    return 0;
}

所以这种按引用传递意味着对方法中变量的更改保存在方法之外。

所以你的代码应该是这样的:

#include <iostream>
void getData(int&first, int&second, int&third){
    std::cout<<"Enter 3 Integer Values: ";
    std::cin>>first>>second>>third;
}
int calcTotal(int first, int second, int third){//Pass as parameters, so the method knows what numbers to add
    return first + second + third;
}//calcTotal returns the total
void printTotal(int total){//printTotal doesn't return anything! printTotal only prints stuff, it doesn't have a numeric result to give you
    std::cout<<"Total: "<<total;
}
int main(){
    int first,second,third;
    getData(first,second,third);
    int total=calcTotal(first,second,third);
    printTotal(total);
    return 0;
}

附言永远永远永远不要在你的代码中使用 using namespace std;。它会导致死亡、破坏和那些认为这是坏事的人的恼人回答。

附言看到你所处的入门级，我建议从 Python 开始。检查出!它更容易学习。