why I got error in MATLAB 2012a " Undefined function or variable 'p'. The first assignment to a local variable determines its class."when i run my code?

//This is my code

function p  = fcn(GLE,s)
coder.extrinsic('pause');
p=p+1;
while (p<=4)
n=GLE;
end;
while ((p==1) && (n>=5)) 
    g1=1;
    r1=0;
    y1=0;
    g2=0;
    r2=1;
    y2=0;
    g3=0;
    r3=1;
    y3=0;
    g4=0;
    r4=1;
    y4=0;
    n=n-1;
    pause (1);
end
    while ((p==1) && (n>0))
    g1=0;
    r1=0;
    y1=1;
    g2=0;
    r2=1;
    y2=0;
    g3=0; 
    r3=1;
    y3=0;
    g4=0;
    r4=1;
    y4=0;
    pause (1)
    n=n-1;
    end;

      if (n==1) 
          a=2;
      end
   p = GLE;
   p=s;

Answer 1

[Steven Lord]

The variable p isn't defined the first time you try to use it in your function, on the line "p = p+1;". What exactly do you think the result of that command should be?

Answer 2

[Walter Roberson]

I speculate that you might want to start with

persistent p
if isempty(p)
  p = 0;
end