C++:::无法调用错误，如 Stroustrup 书中的指示

Question

我决定自己学习 C++，我已经有了一些 Java 经验。

在 Bjarne Stroustrup 的书中他说:

Prompt the user to enter the age of the recipient and assign it to an int variable age. Have your program write "I hear you just had a birthday and You are 'age' years old." If age is 0 or less or 110 or more, call error("you're kidding! ").

在此之前的几页中，他使用错误函数如下:

double d1 = 2.3;

double d2 = d1 + 2;

if (d1 < 0)

error( "d1 is negative");

当我尝试运行我的程序时(Bjarnes 书中的练习)，我得到“使用未声明的标识符‘错误’”。

我曾尝试研究我的问题，但直到现在每次都找到了解决方案，但无济于事。

如果需要，这里是我的 Main.cpp 的内容:

#include <iostream> 
using namespace std;

int main() {

    cout << "Please enter the recipients name: " << endl;
    string rname;
    getline(cin, rname);

    cout << "Ok, thank you. What is your mutual friends name: " <<endl;
    string fname;
    getline (cin, fname);

    cout << "Ok, now what gender is you friends? 'm' for male, and 'f' for female: ";
    char fsex;
    cin >> fsex;

    cout << "Fantastic, now how old is the recipient? " << endl;
    int age;
    cin >> age;
    if(age >= 0 && age <= 110){
        cout << "Thank you " << endl;
    }
    if(age <= 0 && age >= 110){
        error("You're Kidding!");
    }



    return 0; }

Answer 1

你必须包含标题

std_lib_facilities.h

参见 the header definition