Mathematic operations and structures in C

[lewis198]

Hello guys, I was wondering:

say you have a structure:

struct tag{

int a
char b
int b
int c
}

how would you make int c equal to int a + int b for all variables of type struct tag? I have tried using pointers but it baffles me how you would make a global change in that all variable s of type struct tag would be affected, rather than just specific variables.

thank you for your time.

 

[lewis198]

*variables rather than variable s

 

[chroot]

You'd have to perform the assignment t.c = t.a + t.b for every variable of type tag that you create. There is no such thing as a "global change."

If you decide to use C++ features, you can turn this structure into a class, and then use a member function to calculate c, rather than storing it directly.

- Warren

 

[Coin]

If you decide to use C++ features, you can turn this structure into a class, and then use a member function to calculate c, rather than storing it directly.

If you want to do that it would look like:

struct tag{

int a;
char b2;
int b;
int c() { return a + b; }
};

But remember, like chroot said, you cannot do this in C, you must be using C++; also did you notice you have two structure elements named "b"...?

 

[lewis198]

oops, sorry-heehee!

but wow you can do that in c++, i'd better translate

 

[lewis198]

would you have to declare a and b in the meber function c?

 

[lewis198]

*member

 

[chroot]

No, a and b would be class variables (variously called 'member variables,' 'class fields,' 'member fields,' etc.).

- Warren

 

[lewis198]

Hey guys I have a problem. When trying to compile this on dev c++ it wpon't let me, as it says I'm trying to make it a function, and when a change struct to a class, it says error before the class name, as well as calling 'private:' and 'public:' errors.

 

[lewis198]

in fact, my devc++ compiler does not seem to accept any c++ language-when i enter cout it says 'undeclared variable'. Do you guys know what the problem might be?

 

[chroot]

Sounds like the problem is that you don't know C++.

Show us some examples of the code that doesn't work and we'll try to help.

- Warren

 

[Coin]

in fact, my devc++ compiler does not seem to accept any c++ language-when i enter cout it says 'undeclared variable'. Do you guys know what the problem might be?

Did you say #include <iostream>?

If you put "using namespace std;" somewhere near the top of your file, does anything magic happen?

 

[rcgldr]

You mentioned "C", but you're trying to use a "C++" feature. If you want your source code to be compiled as "C++", the file name extension should be "cpp", not "c", such as "example.cpp" instead of "example.c".