Question

以下程序在计算选择后终止，没有任何进一步发生。所以我的问题是我在做什么？请有人检查这个程序并通知我我的错误。该程序是一个计算器，要求用户选择计算方法，即加法，除法或乘法等，然后在计算后显示结果图片：http://i43.tinypic.com/2hykpjp.png 请原谅我，因为我是C编程的新手。

main()
{
  // declaration
  int add,sub,mul,div,selection;
  float a,b,c;
  // prompt user to select a method
  cout << "Calculator, which performs addition,subtraction,multiplication and division: add,sub,mul,div";
  cout << "Please enter your selection (for example: mul): ";
  cin >> selection;
  if (selection = add)
  {
             // prompt user to enter values
             cout << "Please enter first value: ";
             cin >> a;
             cout << "Please enter second value: ";
             cin >> b;
             // calculations
             c = a + b;
             // result
             cout << "Answer: " << c;
  }
  if (selection == sub)
  {
             // prompt user to enter values
             cout << "Please enter first value: ";
             cin >> a;
             cout << "Please enter second value: ";
             cin >> b;
             // calculations
             c = a - b;
             // result
             cout << "Answer: " << c;
  }
  if (selection == mul)
  {
             // prompt user to enter values
             cout << "Please enter first value: ";
             cin >> a;
             cout << "Please enter second value: ";
             cin >> b;
             // calculations
             c = a * b;
             // result
             cout << "Answer: " << c;
  }
  if (selection == div)
  {
             // prompt user to enter values
             cout << "Please enter first value: ";
             cin >> a;
             cout << "Please enter second value: ";
             cin >> b;
             // calculations
             c = a / b;
             // result
             cout << "Answer: " << c;
  }
}

Answer 1

您尚未在此处初始化任何内容：

int add,sub,mul,div,selection;

您使用selection获取cin >> selection;的值，但这些内容应该是什么意思：

if (selection = add)
if (selection == sub)
if (selection == mul)
if (selection == div)

存储类auto的变量未初始化为任何默认值。

Answer 2

以下行没有初始化。

 int add,sub,mul,div,selection;

使用唯一值初始化这些变量（例如0表示添加，1表示sub）。另外，相比之下

 selection = add

使用

selection == add

使用else if代替ifs。它将改善性能。在您的情况下，它将比较每个条件。它显示为一个例子。

  if (selection = add)
     {
                // prompt user to enter values
                cout << "Please enter first value: ";
                cin >> a;
                cout << "Please enter second value: ";
                cin >> b;
                // calculations
                c = a + b;
                // result
                cout << "Answer: " << c;
     }
  else if (selection == sub)
     {
                // prompt user to enter values
                cout << "Please enter first value: ";
                cin >> a;
                cout << "Please enter second value: ";
                cin >> b;
                // calculations
                c = a - b;
                // result
                cout << "Answer: " << c;
     }

//Rest of your program.

Answer 3

根据您运行程序的示例，您要做的是输入字符串，例如添加，然后比较它们。你在程序中实际做的是选择，添加， sub 等等是整数变量，它们只能用于存储整数。

您必须将选择声明为字符串变量，并将其值与字符串常量进行比较，如下所示：

string selection;

然后：

if (selection == "add")

这个程序出了什么问题，终止了？

3 个答案: