Linux compilation error: ' cout ' not yet declared in this scope

Beginners in Linux for C + + programming will encounter "'cout ' in this scope has not been declared " error.

Many people will find it very strange, I am in strict accordance with C + + syntax to write, why also at compile-time prompt "' cout ' in this scope has not declared" error?

The following is a detailed analysis of the causes of the error, through analysis to get the solution to the problem .

First, let's take a piece of code for example.

If we save this code as Hello.cpp

In the terminal input g++ hello.cpp-o Hello

The compiler is sure to quote "' cout ' has not declared an error in this scope."

Error Reason:

#include can not use Cout/cin in the program directly, #include to include the namespace std to directly use cout/cin, otherwise the function/variable defined in the header file should be preceded by std:: to represent the calling function/ The source of the variable.

Solution:
Method One: Under #include add a phrase "using namespace std;"

[CPP] #include <iostream> using namespace std;      int Main (void) { int i;      int n=1; for        (i=0;i<n;i++)          {cout<< "hello\n";        n++; }    }

Method Two: Replace cout with cout std::cout [cpp] #include  <iostream>         int  main ( void )                {       int  i;       int  n=1;       for (i=0;i<n;i++)         {           std::cout<< "hello\n";          n++;        }   }