系统未在范围内声明？

Question

我知道它的简单代码，如何解决“系统未在范围内声明”问题？

#include<iostream>
using namespace std;

int main(void)
{
    system ( "TITLE Calculator" );
    system ( "COLOR 2" );
    char cChar;
    double dfirstnumber;
    double dsecondnumber;
    char cDoagain;

    do
    {
        system("CLS");
        cout << "Please enter the first number you would like to use."<< endl;
        cin >> dfirstnumber;
        cout<< "Please enter the operation you would like to perform." << " (+,-,*,or /)" << endl;
        cin >> cChar;
        cout<< "Please enter the second number you would like to use." << endl;
        cin >> dsecondnumber;

        switch (cChar)
        {
            case '+':
                cout << "The answer is: " << dfirstnumber << "+" << dsecondnumber << "=" <<
                (dfirstnumber + dsecondnumber) << endl;
                break;
            case '-':
                cout << "The answer is: " << dfirstnumber << "-" << dsecondnumber << "=" <<
                (dfirstnumber - dsecondnumber) << endl;
                break;
            case '*':
                cout << "The answer is: " << dfirstnumber << "*" << dsecondnumber << "=" <<
                (dfirstnumber * dsecondnumber) << endl;
                break;
            case 'x':
                cout << "The answer is: " << dfirstnumber << "x" << dsecondnumber << "=" <<
                (dfirstnumber * dsecondnumber) << endl;
                break;
            case 'X':
                cout << "The answer is: " << dfirstnumber << "X" << dsecondnumber << "=" <<
                (dfirstnumber * dsecondnumber) << endl;
                break;
            case '/':
                if(dsecondnumber == 0){
                cout<< "That is an invalid operation." << endl;}
                else{
                cout << "The answer is: " << dfirstnumber << "/" << dsecondnumber << "=" <<
                (dfirstnumber / dsecondnumber) << endl;

        }
                break;
                default:
                    cout << "That is an invalid operation." << endl;
                    break;
    }
                cout << "Would you like to start again? (Y/N)" << endl;
                cin >>  cDoagain;
    }while (cDoagain == 'Y' or cDoagain == 'y');
    system("PAUSE");
    return 0;
}

这是我的结束语：

C:\Documents and Settings\Nilo\My Documents\Work\Testing\main.cpp||In 函数'int main()':| C:\Documents and Settings\Nilo\My Documents\Work\Testing\main.cpp|8|错误：“系统”未在中声明 这个范围||

|=== 构建完成：1 个错误，0 个警告 ===|

Answer 1

您需要添加：

 #include <cstdlib>

以便编译器能够看到 system() 的原型。

Answer 2

您可能没有包含声明 system() 的头文件。

为了能够编译使用您未（手动）自己声明的函数的 C++ 代码，您必须提取声明。这些声明通常存储在所谓的头文件中，您可以使用#include 预处理器指令将其拉入当前翻译单元。由于代码中没有#include声明system()的头文件，因此编译失败。

要解决此问题，请找出哪个头文件为您提供了 system() 声明并将其包含在内。正如其他几个答案中提到的，您很可能需要添加 #include