error C2065: undeclared identifier PLEASE HELP!

dyelax · 10-12-2009, 08:32 AM

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;
		}
	}
}

tabstop · 10-12-2009, 08:49 AM

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.

dyelax · 10-12-2009, 09:21 AM

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

tabstop · 10-12-2009, 09:27 AM

Variable Definition | Definition of Variable at Dictionary.com

Constant Definition | Definition of Constant at Dictionary.com

dyelax · 10-12-2009, 09:47 AM

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

tabstop · 10-12-2009, 09:51 AM

A constant is something like 6. Or 11. Or 253. Something that is constant according to the English sense of the term.

dyelax · 10-12-2009, 09:56 AM

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);

**laserlight** · 10-12-2009, 09:58 AM

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?

dyelax · 10-12-2009, 10:01 AM

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;
		}
	}
}

**laserlight** · 10-12-2009, 10:09 AM

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;
        }
    }
}

dyelax · 10-12-2009, 10:16 AM

ooooohhhhhh. so the case has to be a number?

dyelax · 10-12-2009, 10:24 AM

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

tabstop · 10-12-2009, 10:26 AM

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)

dyelax · 10-12-2009, 11:50 AM

all right thank you

10-12-2009, 08:32 AM	#1
dyelax Registered User Join Date: Oct 2009 Posts: 16	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; } } }
dyelax is offline

10-12-2009, 08:49 AM	#2
tabstop and the Hat of Guessing Join Date: Nov 2007 Posts: 8,740	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.
tabstop is offline

10-12-2009, 09:21 AM	#3
dyelax Registered User Join Date: Oct 2009 Posts: 16	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
dyelax is offline

10-12-2009, 09:27 AM	#4
tabstop and the Hat of Guessing Join Date: Nov 2007 Posts: 8,740	Variable Definition \| Definition of Variable at Dictionary.com Constant Definition \| Definition of Constant at Dictionary.com
tabstop is offline

10-12-2009, 09:47 AM	#5
dyelax Registered User Join Date: Oct 2009 Posts: 16	ya i know that i meant whats the difference in writing them in c++
dyelax is offline

10-12-2009, 09:51 AM	#6
tabstop and the Hat of Guessing Join Date: Nov 2007 Posts: 8,740	A constant is something like 6. Or 11. Or 253. Something that is constant according to the English sense of the term.
tabstop is offline

10-12-2009, 09:56 AM	#7
dyelax Registered User Join Date: Oct 2009 Posts: 16	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);
dyelax is offline

10-12-2009, 10:09 AM	#10
laserlight C++ Witch Join Date: Oct 2003 Location: Singapore Posts: 10,356	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; } } } __________________ C + C++ Compiler: MinGW port of GCC Build + Version Control System: SCons + Bazaar Look up a C/C++ Reference and learn How To Ask Questions The Smart Way
laserlight is online now

10-12-2009, 10:16 AM	#11
dyelax Registered User Join Date: Oct 2009 Posts: 16	ooooohhhhhh. so the case has to be a number?
dyelax is offline

10-12-2009, 10:24 AM	#12
dyelax Registered User Join Date: Oct 2009 Posts: 16	thank you! it runs now! I'm sorta confused why you dont have to have "int a;" at the beginning before the loop
dyelax is offline

10-12-2009, 10:26 AM	#13
tabstop and the Hat of Guessing Join Date: Nov 2007 Posts: 8,740	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)
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10-12-2009, 11:50 AM	#14
dyelax Registered User Join Date: Oct 2009 Posts: 16	all right thank you
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