使用 C++ 编译问题 [关闭]

Posted 2023-02-22

【中文标题】使用 C++ 编译问题 [关闭]

【英文标题】：Compiling Issue with C++ [closed]

【发布时间】：2019-06-21 00:02:43

【问题描述】：

我刚开始学习 C++ 课程，我们的第一个任务是一个简单的代码，它利用了用户提供的变量。当我尝试编译代码时，我不断收到一些语法错误，但根据课程的书（和其他在线资源），我认为我的语法是正确的。有什么见解吗？

编辑：澄清一下，我意识到我的语法是错误的，因为编译器会抛出错误，我只是不确定我错在哪里。感谢我收到的所有帮助。

代码：

//SP2019_Lab1Part2_Key.cpp

#include <iostream>
#include <string>
#include <sstream>
using namespace std;


cout << string(50, '-') << endl;
cout << "SP2019_Aaron Key - OUTPUT OF USING VARIABLES" << endl;
//declares string variable "Word"
char Word;
//Prompts user for word:
cout << "Word: ";
//Waits for input for value of "Word" from standard input (keyboard)
cin << Word;

//Declares integer variable "FirstNumber"
double FirstNumber;
//Prompts user for a number:
cout << "First Number: ";
//Waits for number:
cin << FirstNumber;

//Declares double variable "SecondNumber":
double SecondNumber;
//Prompts user for a number:
cout << "Second Number: ";
//Waits for input:
cin << SecondNumber;

//Adds FirstNumber and SecondNumber:
double SUM = FirstNumber + SecondNumber;
//Calculates Average of FirstNumber and SecondNumber:
double Avg = SUM / 2;


//Gives the average of FirstNumber and SecondNumber:
stringstream calavg;
calavg << "The average of " << FirstNumber << " and " << SecondNumber 
<< " is: " << Avg;
cout <<  char calavg.str();
cout << string(50, '-') << endl;

错误：

Microsoft (R) C/C++ Optimizing Compiler Version 19.16.27026.1 for x86
Copyright (C) Microsoft Corporation.  All rights reserved.

SP2019_Lab1Part2_Key.cpp
SP2019_Lab1Part2_Key.cpp(9): error C2143: syntax error: missing ';' before '<<'
SP2019_Lab1Part2_Key.cpp(9): error C4430: missing type specifier - int assumed. Note: C++ does not support default-int
SP2019_Lab1Part2_Key.cpp(10): error C2143: syntax error: missing ';' before '<<'
SP2019_Lab1Part2_Key.cpp(10): error C4430: missing type specifier - int assumed. Note: C++ does not support default-int
SP2019_Lab1Part2_Key.cpp(10): error C2086: 'int cout': redefinition
SP2019_Lab1Part2_Key.cpp(9): note: see declaration of 'cout'
SP2019_Lab1Part2_Key.cpp(14): error C2143: syntax error: missing ';' before '<<'
SP2019_Lab1Part2_Key.cpp(14): error C4430: missing type specifier - int assumed. Note: C++ does not support default-int
SP2019_Lab1Part2_Key.cpp(14): error C2086: 'int cout': redefinition
SP2019_Lab1Part2_Key.cpp(9): note: see declaration of 'cout'
SP2019_Lab1Part2_Key.cpp(16): error C2143: syntax error: missing ';' before '<<'
SP2019_Lab1Part2_Key.cpp(16): error C4430: missing type specifier - int assumed. Note: C++ does not support default-int
SP2019_Lab1Part2_Key.cpp(21): error C2143: syntax error: missing ';' before '<<'
SP2019_Lab1Part2_Key.cpp(21): error C4430: missing type specifier - int assumed. Note: C++ does not support default-int
SP2019_Lab1Part2_Key.cpp(21): error C2086: 'int cout': redefinition
SP2019_Lab1Part2_Key.cpp(9): note: see declaration of 'cout'
SP2019_Lab1Part2_Key.cpp(23): error C2143: syntax error: missing ';' before '<<'
SP2019_Lab1Part2_Key.cpp(23): error C4430: missing type specifier - int assumed. Note: C++ does not support default-int
SP2019_Lab1Part2_Key.cpp(23): error C2086: 'int cin': redefinition
SP2019_Lab1Part2_Key.cpp(16): note: see declaration of 'cin'
SP2019_Lab1Part2_Key.cpp(28): error C2143: syntax error: missing ';' before '<<'
SP2019_Lab1Part2_Key.cpp(28): error C4430: missing type specifier - int assumed. Note: C++ does not support default-int
SP2019_Lab1Part2_Key.cpp(28): error C2086: 'int cout': redefinition
SP2019_Lab1Part2_Key.cpp(9): note: see declaration of 'cout'
SP2019_Lab1Part2_Key.cpp(30): error C2143: syntax error: missing ';' before '<<'
SP2019_Lab1Part2_Key.cpp(30): error C4430: missing type specifier - int assumed. Note: C++ does not support default-int
SP2019_Lab1Part2_Key.cpp(30): error C2086: 'int cin': redefinition
SP2019_Lab1Part2_Key.cpp(16): note: see declaration of 'cin'
SP2019_Lab1Part2_Key.cpp(40): error C2143: syntax error: missing ';' before '<<'
SP2019_Lab1Part2_Key.cpp(40): error C4430: missing type specifier - int assumed. Note: C++ does not support default-int
SP2019_Lab1Part2_Key.cpp(40): error C2371: 'calavg': redefinition; different basic types
SP2019_Lab1Part2_Key.cpp(39): note: see declaration of 'calavg'
SP2019_Lab1Part2_Key.cpp(41): error C2143: syntax error: missing ';' before '<<'
SP2019_Lab1Part2_Key.cpp(41): error C4430: missing type specifier - int assumed. Note: C++ does not support default-int
SP2019_Lab1Part2_Key.cpp(41): error C2086: 'int cout': redefinition
SP2019_Lab1Part2_Key.cpp(9): note: see declaration of 'cout'
SP2019_Lab1Part2_Key.cpp(42): error C2143: syntax error: missing ';' before '<<'
SP2019_Lab1Part2_Key.cpp(42): error C4430: missing type specifier - int assumed. Note: C++ does not support default-int
SP2019_Lab1Part2_Key.cpp(42): error C2086: 'int cout': redefinition
SP2019_Lab1Part2_Key.cpp(9): note: see declaration of 'cout'

【问题讨论】：

" 我认为我的语法是正确的。" 编译器告诉你不是。

他们没有教你main函数吗？您不能只在文件范围内编写代码。

using namespace std;

我正在上一门在线课程，本书的第一章（作业应该与此一致）只讨论了伪代码，以及用伪代码思考的重要性.对于这样的问题更“热门”的在线论坛，您有什么建议吗？

【参考方案1】：

你在这里犯了一些错误：

您必须在int main() 中编写整个主代码 使用 cin 的语法是 cin >> 而不是 cin << 您不需要将char 放在calavg.str() 之前，因为它已经声明为字符串流 不要使用using namespace std。这是一种不好的做法，可能会导致库冲突Why is "using namespace std" considered bad practice?

代码：

#include <iostream>
#include <string>
#include <sstream>

int main()

    std::cout << "SP2019_Aaron Key - OUTPUT OF USING VARIABLES" << std::endl;
    //declares string variable "Word"
    char Word;
    //Prompts user for word:
    std::cout << "Word: ";
    //Waits for input for value of "Word" from standard input (keyboard)
    std::cin >> Word;

    //Declares integer variable "FirstNumber"
    double FirstNumber;
    //Prompts user for a number:
    std::cout << "First Number: ";
    //Waits for number:
    std::cin >> FirstNumber;

    //Declares double variable "SecondNumber":
    double SecondNumber;
    //Prompts user for a number:
    std::cout << "Second Number: ";
    //Waits for input:
    std::cin >> SecondNumber;

    //Adds FirstNumber and SecondNumber:
    double SUM = FirstNumber + SecondNumber;
    //Calculates Average of FirstNumber and SecondNumber:
    double Avg = SUM / 2;


    //Gives the average of FirstNumber and SecondNumber:
    std::stringstream calavg;
    calavg << "The average of " << FirstNumber << " and " << SecondNumber 
    << " is: " << Avg;
    std::cout <<  calavg.str();

    return 0;

【讨论】：

好的，我将编辑帖子..实际上使用命名空间std更容易被初学者理解，每个编程讲座都在开始时使用该命名空间（至少对我而言）

@gameon67 "其实使用命名空间std对于初学者来说更容易理解，每一堂编程课一开始都使用那个命名空间" 值得商榷。在最初的学习阶段之后，改掉使用using namespace std; 的习惯比理解命名空间的概念（不是细节，而是概念本身）更难。然而，大多数讲师往往只是不打扰。相关阅读：Why is “using namespace std” considered bad practice?

已编辑。我同意伙计们。使用命名空间 std 是一个非常糟糕的习惯。我想我刚上大学时的编程课很糟糕

哇，谢谢大家！我不知道 using namespace std - 很多在线参考推荐它，所以我认为它只是一个方便的小功能。

@akey 第一个月学习编程，很方便。但是当你进入更大的项目时，这是很危险的。也请接受我的回答:)