Error useing a string in more files

[CosminPerRam]

Hello there, i have soem problems with my code and i dont know how to fix it, you can help me? Thanks in advance.

There's the problem:

main.cpp:



#include <iostream>
#include <string>
#include "second.h"

using namespace std;

int main()
{
    string w;
    cin >> w;
    char c = w.at(0);
    cout<<c<<endl;
    eloop();
}

second:

#include <iostream>
#include "second.h"

using namespace std;

void eloop()
{
if(c=='a')
{
cout<<"There's an a"<<endl;
}
return;

And i got this error:

F:\Projects\C++\Code Blocks\Mine\PR Encrypt messages\src\econd.cpp|8|error: 'c' was not declared in this scope|

How to tell it to be in ALL?
Thanks in advance!

[shadder]

Hi,

well the compiler said that 'c' was not declared in scope because it wasn't

you may declare char c globally or use a function and point it

[CosminPerRam]

Sorry, but i dont understand how to do it, you can give me an example? Thanks in advance

[shadder]

for starters just declare w and c in second: and see if it works

[CosminPerRam]

If i get w and c in global in the second one it will auto crash the program, if i call it in local and press anything, after enter it will crash like in the first one, its an long error here.

[shadder]

could you tell what and where at() function is? I don't know about it

[E0p9LyTq]

All you need to do is rewrite your eloop() function:

main.cpp:

#include <iostream>
#include <string>
#include "second.h"

int main()
{
   std::cout << "Enter a string: "; 
   std::string w;
   std::cin >> w;
   char c = w.at(0); // or char c = w[0];
   
   std::cout << c << "\n";

   eloop(c);
}

second.h:

#ifndef __SECOND_H__
#define __SECOND_H__

void eloop(char c);

#endif 

second.cpp:

#include <iostream>
#include "second.h"

void eloop(char c)
{
   if (c == 'a' || c == 'A')
   {
      std::cout << "The first letter's an a\n";
   }
}

Enter a string: Attack!
A
The first letter's an a

[jlb]

could you tell what and where at() function is? I don't know about it

The at() function, in this case, is a member function of the standard C++ class string. Perhaps you need to study the documentation for this standard C++ class.

[shadder]

could you provide any links?

[E0p9LyTq]

As others suggested you could declare char c globally:

main.cpp:

#include <iostream>
#include <string>
#include "second.h"

char c; // declare c here as a global

int main()
{
   std::cout << "Enter a string: "; 
   std::string w;
   std::cin >> w;
   c = w.at(0);
   
   std::cout << c << "\n";

   eloop();
}

And then tell the compiler the variable can be used by other .cpp files. second.h:

#ifndef __SECOND_H__
#define __SECOND_H__

void eloop();

extern char c;  // notice the use of extern!

#endif 

http://en.cppreference.com/w/cpp/language/storage_duration

second.cpp:

#include <iostream>
#include "second.h"

void eloop()
{
   if (c == 'a' || c == 'A')
   {
      std::cout << "The first letter's an a\n";
   }
}

[jlb]

could you provide any links?

Is your "Google" broken?

[E0p9LyTq]

@p007:
http://www.cplusplus.com/reference/string/basic_string/at/

and:

http://en.cppreference.com/w/cpp/string/basic_string/at

BTW, as jlb suggested there is an entire REFERENCE section here at cplusplus, stuffed full of examples:
http://www.cplusplus.com/reference/

[shadder]

thanks :)

[48T7M4Gy]

#include <iostream>
#include <string>

void eloop(char);

int main()
{
    std::string w = "?";
    std::cin >> w;
    char c = w.at(0);
    std::cout << c << std::endl;
    eloop(c);
}

void eloop(char aChar)
{
    if( aChar =='a' )
        std::cout << "There's an a" << std::endl;
    else
        std::cout << "There's no a" << std::endl;
    return;
}

apple
a
There's an a

banana
b
There's no a

[CosminPerRam]

I fixed my problem, thanks so much!