为什么是“cout”？功能不起作用？ [英] why is the "cout" function not working in functions?

问题描述

大家好，

我是初学者，对代码有一个小问题。

编译器标出错误说： -

hello everyone,
i'm a beginner and have a small problem regarding a code.
the compiler flags an error saying:-

error C2065: 'cout' : undeclared identifier

这里是代码

here is the code

char downer(char[13])
{
cout<<"hello";
}

using namespace std;

int main()
{
char ocean[13];
puts(" please enter the name of the ocean ");
cin>>ocean;
downer(ocean);
}

请帮我处理这个错误。



这里是一个指向整个代码的链接（以防万一你需要改写它）

链接 [ ]

推荐答案

问题与无关函数。

您应该使用 #include< iostream> 以及使用命名空间std ：

The problem has nothing to do with "functions".
You should use #include <iostream> and also using namespace std:

#include <iostream>
using namespace std;

//...

void SomeFunction(/* ... */)
{
    cout << "Now working!";
    //... 
}

//...

您还需要了解命名空间的工作原理，以及可能还有很多。







我可以看到问题的变化。不过，它需要修复。该代码缺少 #include< iostream> 。现在，代码将无法编译，因为 downer 不会返回任何内容。因此，将返回类型更改为 void 。并且该函数的参数毫无意义，将其从函数定义和调用中删除。 （将来，您可能需要 char * 参数，以传递不指定其长度的字符串;通常，在C和C ++中，使用以null结尾的字符串。）



这就是全部。







正如Stefan_Lang指出的那样，不使用使用命名空间有很多好处。您可以使用完全限定名称。这种方式排除了名称冲突，并且 - 在这种情况下非常重要 - 促进了解真实情况。



上面显示的输出行看起来像

You also need to learn how namespaces work, and probably a lot more.



I can see the changes in the question. Still, it need fixes. The code lacks #include <iostream>. Now, the code won't compile, because downer does not return anything. So, change return type to void. And parameter of this function is pointless, removed it from function definition and the call. (In future, you may need char* parameter, to pass a string without specification of its length; usually, in C and C++, null-terminated string is used.)

That's all.



As Stefan_Lang pointed out, there is are considerable benefits of not using "using namespace". You can use fully-qualified names instead. This way excludes name clash, and — very important in this very case — promotes understanding of what really goes on.

The output line shown above will look like

std::cout << "Working without using namespace";

祝你好运，

-SA

我已经重写了你的代码，所以你可以看到你的错误。



在此之前，由于我认为，根据您的代码，您熟悉C语言的一小部分解释，因此这些解释可能对您有所帮助：



让我们从你的功能开始吧。



既然你只想在控制台上写点东西，使用cout，你不需要返回值（参见代码中的注释，char在void中更改）。



此外，我已将cout语句更改为输出您传递给函数的海洋字符串，请参阅代码。



您已经以错误的方式将字符串传递给函数downer，我已经更改了也好。



忘掉看跌期权，改用cout，我已经改变了也是代码。



我使用double作为带小数点的变量的类型，而不是浮点数，请参阅代码。



我在代码的最后添加了return语句，这表示main退出时没有错误。



在我看来你知道C并尝试学习C ++。我希望这段代码可以帮到你，如果你需要发表评论，我会帮助你。



最后，代码：

I have rewritten your code, so you can see your mistakes.

Before that, a small set of explanations, since I believe, based on your code, that you are familiar with C, so these explanations might help you:

Let us start with your function.

Since you just want to write something to the console, using cout, you do not need the return value ( see the comments in the code, char is changed in void ).

Also, I have changed cout statement to output the ocean string, that you have passed to the function, see the code.

You have passed the string to the function downer in a wrong way, I have changed that too.

Forget about puts, use cout instead, I have changed that in my code too.

Instead of float, I have used double as a type for your variables with decimal points, see the code.

I have added return statement at the very end of the code, this signals that main exited without error.

It seems to me that you know C and try to learn C++. I hope that this code will help you, if you need anything just post a comment, and I will help you.

Finally, the code:

#include<iostream>
     
using namespace std;
   
void downer( char* test) // <-- this is how you pass a string to a function
{
        // endl just tells cout to go to new line, it is like '\n' in C

	cout<<"hello kaka" << endl << test<< endl;
}
     
int main()
{
	char ocean[13]; 

	int boats,fiiden;

        // use double instead of float for decimal numbers

	double poden=11.29387,inden=12.989,atden=10.28172,arden=9.192772;
        
	cout << " this program calculates the number of fish in any specified ocean " << endl;

        // no need for puts, use cout instead

	cout << " please enter the name of the ocean " << endl;
        
	cin >> ocean;
        
	downer( ocean );

        return 0; // this indicates that main exited successfully without errors!
}

因为您忘记包含头文件...

尝试：

Because you forgot to include the header file...
Try:

#include <iostream>

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