Cant create object in C++

[Carlis]

Hi. I am trying to create an object in c++ but I'm doing terrible. I have tried the following code;

#include <iostream>
#include <fstream>
#include <math.h>


int main (int argc, char * const argv[]) {
using namespace std;

tst test; //error! tst was not declared in this scope. & expected ';' before test end comment//

double a=tst.input(9);
cout << a;

return 0;
}
//--------- tst.cpp

class tst{
public:
double input(double d);
};
double tst::input(double d){
return(d+1);
}

What did I miss?

 

[nickbits]

this:
class tst{
public:
double input(double d);
};

needs to be in a .h file and #included in your main file

 

[mundane]

For your example, it literally *cannot* find the definition of "tst" (it doesn't automatically look ahead). To fix this, either place the definition in an external file and #include it, or move its declaration above your main method.

 

[Markbnj]

As the others have said, it's the order of your declarations. It's best to learn to think of C/C++ files like the compiler sees them: read from top to bottom, and when you encounter #include treat the referenced file as if its contents replaced the "#include" in the text. Any name that you haven't encountered as you read from top to bottom, pulling in the included files, is a name that the compiler doesn't know about either.

 

[degibson]

Do this instead:

#include <iostream>
#include <fstream>
#include <math.h>

class tst{
public:
double input(double d);
};

int main (int argc, char * const argv[]) {
using namespace std;

tst test; //error! tst was not declared in this scope. & expected ';' before test end comment//

double a=tst.input(9);
cout << a;

return 0;
}

//--------- tst.cpp


double tst::input(double d){
return(d+1);
}

... or better yet put the class declaration into test.h and #include as others have suggested.