Hello friends,I suddenly come across an once neglected problem:
If you define a variable in sequence like below
int a=1;
int a=2;
then the error message saying "duplicate" will appear.

But when I write in this way,say,in a loop:

for(int i=0;i<2;i++)
{
int g=1;//here no duplicate?
println(g);
//i+=1;
}

It works.It seems that g is defined the same way as in the former example,but no duplicate error pop up.What's the reason?Any advice is appreciated,thank you in advance.

If you have specified
int g = 0;
outside the for loop then it is true that you now have 2 variables called g and it will compile and run.

The 2 vaiables can store different values but inside the loop it will use the g variable declared inside the loop and when outside the loop it will use the one declared outside the loop.

Care should be used when using variables with the same name because it can cause confusion when programming about which one is being used.

JScriptChan wrote on Apr 19^th, 2009, 10:38pm:


The compiler checks syntax, if it were to actually run the code, you may get the duplicate error, but because it is inside the for loop, the syntax looks correct to the compiler (ie. the compiler doesn't run the loop). However, as mentioned, the value of g will be 1 and not available outside the for loop. So if you were to use it outside the loop,

for(int i=0;i<2;i++)
{
int g=1;//here no duplicate
println(g);
//i+=1;
}
if(g)
{}

you will get a compile error, so to prevent that error you will need to declare it outside the loop,

int g;
for(int i=0;i<2;i++)
{
int g=1;//here no duplicate
println(g);
//i+=1;
}
if(g)
{}

Now you will get your duplicate error, and to correct it,
Edit
Depending on the compiler, you may not get the duplicate error as the int g outside the loop will be a different variable than that inside the loop, but this is good for visualization

int g;
for(int i=0;i<2;i++)
{
g=1;
println(g);
//i+=1;
}
if(g)
{}

JScriptChan wrote on Apr 22^nd, 2009, 3:26am:


Not necessarily inside just a for loop - it's any time you add a scope, or a set of {}.

This might help a little bit http://www.noobscorner.jassper.com/frm_scope.htm

It is a short explanation for a different language, nwscript, but the concept is the same.

After reading that, basically you can do this,

Code:

void draw()
{ // << Main scope
    int i;
    int x = 10;
    for(i=0; i < x; i++)
	  { // << New scope
	  int x = 1;
	  }
}
 

The loop will still run 10 times because the int x inside the scope for the loop is a different variable than the x in the main scope.

However - no matter what your reasoning is, I strongly recommend that you do not do this! Always name variables differently - it will save your hair on your head in the long run. There is never a case where different variables need to have the same name and even if there is, it would be extremely rare.