error C2065: undeclared identifier PLEASE HELP!

This is a discussion on error C2065: undeclared identifier PLEASE HELP! within the C++ Programming forums, part of the General Programming Boards category; ok so im trying to learn switch cases so i tried to write this program to see if i understood ...

  1. #1
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    error C2065: undeclared identifier PLEASE HELP!

    ok so im trying to learn switch cases so i tried to write this program to see if i understood how to write them and i wrote both my variables the same exact way and its only giving me an undeclared variable for 1 of them. here's my code, please help.

    Code:
    #include <iostream>
    
    using namespace std;
    
    int main ()
    {
    	int a;
    	int b (b = 1);
    	int c (c = 2);
    
    	for (a = 0; a < 3; a++) {
    		switch (a) {
    			case b:
    				{
    					cout<< "wow this is really confusing\n";
    				}
    				break;
    			case c:
    				{
    					cout<< "now it's a little easier\n";
    				}
    				break;
    			default:
    				{
    					cout<< "X-P\n";
    				}
    				break;
    		}
    	}
    }

  2. #2
    and the Hat of Guessing tabstop's Avatar
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    I think you mean
    Code:
    int b(2);
    and similarly for c. Also I don't believe you can use variables in case statements, only constants.

  3. #3
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    thank you so should that part of the code look like

    Code:
    int a;
    int b(1);
    int c(2);
    i tried compiling that and it said "case expression not constant." for both b and c.

    whats the difference between variables and constants? sorry im a beginner haha

  4. #4

  5. #5
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    ya i know that i meant whats the difference in writing them in c++

  6. #6
    and the Hat of Guessing tabstop's Avatar
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    A constant is something like 6. Or 11. Or 253. Something that is constant according to the English sense of the term.

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    yeah so how would i write it because when i write it like this it says "case expression not constant."

    Code:
    int a;
    int b(1);
    int c(2);

  8. #8
    C++ Witch laserlight's Avatar
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    Quote Originally Posted by dyelax
    yeah so how would i write it because when i write it like this it says "case expression not constant."
    What are you trying to do?
    Quote Originally Posted by Bjarne Stroustrup (2000-10-14)
    I get maybe two dozen requests for help with some sort of programming or design problem every day. Most have more sense than to send me hundreds of lines of code. If they do, I ask them to find the smallest example that exhibits the problem and send me that. Mostly, they then find the error themselves. "Finding the smallest program that demonstrates the error" is a powerful debugging tool.
    Look up a C++ Reference and learn How To Ask Questions The Smart Way

  9. #9
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    this is the whole code:

    Code:
    #include <iostream>
    
    using namespace std;
    
    int main ()
    {
    	int a;
    	int b(1);
    	int c(2);
    
    	for (a = 0; a < 3; a++) {
    		switch (a) {
    			case b:
    				{
    					cout<< "wow this is really confusing\n";
    				}
    				break;
    			case c:
    				{
    					cout<< "now it's a little easier\n";
    				}
    				break;
    			default:
    				{
    					cout<< "X-P\n";
    				}
    				break;
    		}
    	}
    }

  10. #10
    C++ Witch laserlight's Avatar
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    What your compiler is trying to tell you is that the expression used in a case must be a constant, i.e., you should write:
    Code:
    #include <iostream>
    
    using namespace std;
    
    int main()
    {
        for (int a = 0; a < 3; a++) {
            switch (a) {
            case 1:
                {
                    cout<< "wow this is really confusing\n";
                }
                break;
            case 2:
                {
                    cout<< "now it's a little easier\n";
                }
                break;
            default:
                {
                    cout<< "X-P\n";
                }
                break;
            }
        }
    }
    Quote Originally Posted by Bjarne Stroustrup (2000-10-14)
    I get maybe two dozen requests for help with some sort of programming or design problem every day. Most have more sense than to send me hundreds of lines of code. If they do, I ask them to find the smallest example that exhibits the problem and send me that. Mostly, they then find the error themselves. "Finding the smallest program that demonstrates the error" is a powerful debugging tool.
    Look up a C++ Reference and learn How To Ask Questions The Smart Way

  11. #11
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    ooooohhhhhh. so the case has to be a number?

  12. #12
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    thank you! it runs now! I'm sorta confused why you dont have to have "int a;" at the beginning before the loop

  13. #13
    and the Hat of Guessing tabstop's Avatar
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    You do have to have int a before the loop.(*) And since you have it, everybody's happy.

    (*)You are allowed to have it inside the loop itself, as in
    Code:
    for (int a = 0; a < 3; ++a)

  14. #14
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    all right thank you

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