I have a simple class here with a variable. Why does it not return the value of the variable 10.5?
Test! -1.09356e+09
#include "iostream"
using namespace std;
class Txtbin{
protected:
float area;
public:
Txtbin();
float get_area();
};
Txtbin::Txtbin(){
float area = 10.5;
}
float Txtbin::get_area(){
return area;
}
int main(int argc, char* argv[]){
Txtbin a;
cout << "Test! " << a.get_area() << endl;
return 0;
}
This is creating a local variable, not initializing your member:
Txtbin::Txtbin(){
float area = 10.5; // creates a variable called area that isn't used.
}
You should initialize your member like this
Txtbin::Txtbin()
: area(10.5)
{
}
Or perhaps directly in the class if you are using C++11 or newer:
class Txtbin{
protected:
float area = 10.5;
public:
Txtbin();
float get_area();
};
txtbin.cpp:11:16: warning: non-static data member initializers only available with -std=c++11 or -std=gnu++11 float area = 10.5; 
Your new area declaration here shadows the member.
Txtbin::Txtbin(){
float area = 10.5;
}
If you enable more/all warnings, the compiler will probably tell you as much.
e.g.
$ clang++ -Weverything tmp/foo.cpp
tmp/foo.cpp:16:11: warning: declaration shadows a field of 'Txtbin' [-Wshadow]
float area = 10.5;
^
tmp/foo.cpp:8:15: note: previous declaration is here
float area;
^
tmp/foo.cpp:16:11: warning: unused variable 'area' [-Wunused-variable]
float area = 10.5;
^
tmp/foo.cpp:23:14: warning: unused parameter 'argc' [-Wunused-parameter]
int main(int argc, char* argv[]){
^
tmp/foo.cpp:23:26: warning: unused parameter 'argv' [-Wunused-parameter]
int main(int argc, char* argv[]){
^
4 warnings generated.
Instead do this, use a member initializer in the constructor.
class Txtbin{
protected:
float area;
public:
Txtbin();
float get_area();
};
Txtbin::Txtbin()
: area(10.5) {
}
Test! 0.