declaration

This is a discussion on declaration within the C Programming forums, part of the General Programming Boards category; Hi, yesterday i tried this Code: #include <stdio.h> #include <stdlib.h> int main() { int x = 0; if (x ==0) ...

  1. #1
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    declaration

    Hi, yesterday i tried this
    Code:
    #include <stdio.h>
    #include <stdlib.h>
    
    int main()
    {
        int x = 0;
    
        if (x ==0)
         int y = 1;
    
        int z = y+x;
        printf("%d",z);
        getchar();
        return 0;
    }
    I am not very good at scope. But from what i understood about scope is it will have a difference scope if the declaration is outside of main.

    However in this case, i am declaring 'y' in the main() function, and why is it still saying that y is not declared in scope?

    Thanks

  2. #2
    Captain Crash brewbuck's Avatar
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    Quote Originally Posted by valthyx View Post
    However in this case, i am declaring 'y' in the main() function, and why is it still saying that y is not declared in scope?
    No, you're declaring it within the scope of the surrounding if-statement. It would be more obvious if you had used curly braces. Think about it -- if x had not been 0, then the "int y" line would not be hit, so now you have a variable that either exists or doesn't exist based on the value of some runtime data, which is impossible.
    Code:
    //try
    //{
    	if (a) do { f( b); } while(1);
    	else   do { f(!b); } while(1);
    //}

  3. #3
    C++ Witch laserlight's Avatar
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    Quote Originally Posted by valthyx
    However in this case, i am declaring 'y' in the main() function, and why is it still saying that y is not declared in scope?
    Because your if statement introduces another block with scope. In this case, that block of scope consists of just one statement. Perhaps using braces will clarify:
    Code:
    #include <stdio.h>
    #include <stdlib.h>
    
    int main()
    {
        int x = 0;
    
        if (x ==0)
        {
            int y = 1;
        }
    
        int z = y+x;
        printf("%d",z);
        getchar();
        return 0;
    }
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  4. #4
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    Is there any other way to declare or make it available globally?

    Or can i use y as a pointer here? So that it could be accessed outside the if scope.

  5. #5
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    Declaring y as a pointer will not change its scope. A pointer is a variable which is used to contain addresses.

    Another good practice would be to declare all the variables just after main so that it becomes available to the entire main block. Something like this

    [insert]
    Code:
    int main(void)
    {
    
       int x, y, z;
       float a,b;
       
       // body of other conditions like if-else
    
       return 0;
    }
    Also you can declare variables outside the main that makes it global . But AFAIK its not a good practice.

  6. #6
    Registered User slingerland3g's Avatar
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    Use extern keyword.

  7. #7
    C++ Witch laserlight's Avatar
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    Quote Originally Posted by roaan
    Another good practice would be to declare all the variables just after main so that it becomes available to the entire main block.
    That is not necessarily a good practice. Rather, declare variables near first use (and thus in the most restricted scope necessary), and if one may not declare variables mixed with code, then declare the variables at the start of the block in which they are first used. In this case, the block where y is first used is that of the main function, so declaring y at the start of the main function is fine.
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    @ Laserlight

    Thanks for correcting :-)

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