global variable is reset after change

http://bit.ly/Vv8fFg

http://e2e.ti.com/support/microcontrollers/msp430/f/166/p/229030/876465.aspx#876465

The first line of main is "b==1;". If you want to set b to 1 then it should be "b=1;"

I'm not sure what's going on with the other variable/function, it'd be helpful if you would post the definition of function foo.

harry han said:

I am totally new to msp430 and CCS

No offense, but most probably you are totally new to C programming language either :)

harry han said:

Could anyone help ?

Reading C books will help you. When you are done reading and know at least basics of programming using C language, then come here to talk about msp430 hardware.

oops thanks to point out my typo :)

llmars said:

Hi llmars

To be honest, I dont think you understand the question I have here. 

And I take your 2nd quote as offense, because from what i am understanding, there is no program level requirement to post on this forum. And since you mentioned reading c books, i have to ask which books you have finish to make you think you are skilled enough to answer for questions :)

Thanks,

Harry

thanks, the links are very helpful :)

harry han said:

To be honest, I dont think you understand the question I have here. 

I clearly understood your question. And it had nothing to do with msp430 microcontroller this forum is about. Your question was basic C programming question, not related to any particular piece of hardware at all. That's why I became little sarcastic. Apologies & peace.

Books.. Can't name any particular one because it was looong time ago, they all are gone. For me when I was learning I was looking for books with lot of examples, snippets you can play with compiling them. I suggest to do some Amazon.com searches, look reviews of most popular books and see wat's more suited for you.

Here's some suggested 'C' learning & reference resources - including books:

http://blog.antronics.co.uk/2011/08/08/so-youre-thinking-of-starting-with-c/

hi llmars

Let me explain the question so you could understand it, because it is not a C problem.....

char a = 5;                    

int main ( void ) {

    char b = 0;

    if( a == 5 ){

        b == 1;   

    }

    if( b == 1 ){

        a = 0;

    }

}

Free run result:

a = 0 b = 1

Single step result:

a = 6( something changed it in the memory when pc enter main ) b =0 

so i am asking what changed variable a in the background and how to avoid it.

llmars, I appropriate your help but i really dont think you understand the question.

Harry

harry han said:

Let me explain the question so you could understand it, because it is not a C problem.....

Well, ok, this is not language-related but knowing your compiler, libraries and debugger. Besides (repeated) b variable assignment typing error you are not paying attention to C start-up routine which initializes global variables. Different compilers can use different naming for it, but common name is cstartup() or _cstartup(). This function is execute _before_ main(). When you run debugger in single step mode, most probably you somehow avoid execution of cstartup() or debugger is configured to not run it, a is not initialized in result. You shall check debugger options first, if nothing there then simply look for function, place breakpoint in it, debug.

harry han said:

From what I see from debuger, a is never set to zero, and foo() is not called. b cannot be set to 1 but keep as a random value( like 0x02)

The above main code (assuming that there is no ohter sourcecode in the same C file) can be reduced to

int main(void){ foo(); }

Which probably is what the compiler does.

If a and b weren't static (but global then and visible outisde the current C file) or used somewhereelse in teh same source file, things would be different.

harry han said:

it is not a C problem.....

Maybe not 'C' specifically, but you still seem to be making false assumptions about compiled, high-level language code - in particular, the likelihood that a compiler will optimise-out stuff that is clearly pointless.

The chances are that what you're looking at in the debugger is not actually variables 'a' and 'b' - because those variables will have been optimised away.

harry han said:

Free run result:

What does that actually mean? You program produces no result - it exits main (which, in this context, is an error in itself) but does not specify a return value.

How and at what point do you evaluate/inspect this "result"?

harry han said:

Single step result:

Again, what does that mean? How and at what point do you evaluate/inspect this "result"?