Beginner's question on methods

ruby-talk
1

I'm new to Ruby, having worked with Perl the past couple of years. I'm
having trouble calling a method to increment a counter, and I'm assuming
that the problem is with the scope of the variables?

I'm getting the following error message:
P:/PETERV2/scripts/vlog2.rb:25:in `test_meth1': undefined method `+' for
nil:NilClass (NoMethodError)
  from P:/PETERV2/scripts/vlog2.rb:47
  from P:/PETERV2/scripts/vlog2.rb:36:in `each'
  from P:/PETERV2/scripts/vlog2.rb:36
  from P:/PETERV2/scripts/vlog2.rb:7:in `open'
  from P:/PETERV2/scripts/vlog2.rb:7

This is the method I'm trying to call:
def test_meth1
   counter = counter + 1
   return counter
end

This is the call:

          case typrec # case statement
example.
             when "TR001"
                 cntr = test_meth1
                 puts cntr # Here I want to print the counter value.
             when "AB001"
                ab001 += 1
             when "AI001"
                ai001 += 1
             else
                puts "Invalid message type"
          end

I assume that there's a really simple mistake I'm making, so any help
would be greatly appreciated.

···

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2

Peter Vanderhaden wrote:

I'm new to Ruby, having worked with Perl the past couple of years. I'm
having trouble calling a method to increment a counter, and I'm assuming
that the problem is with the scope of the variables?

I'm getting the following error message:
P:/PETERV2/scripts/vlog2.rb:25:in `test_meth1': undefined method `+' for
nil:NilClass (NoMethodError)
  from P:/PETERV2/scripts/vlog2.rb:47
  from P:/PETERV2/scripts/vlog2.rb:36:in `each'
  from P:/PETERV2/scripts/vlog2.rb:36
  from P:/PETERV2/scripts/vlog2.rb:7:in `open'
  from P:/PETERV2/scripts/vlog2.rb:7

This is the method I'm trying to call:
def test_meth1
   counter = counter + 1
   return counter
end

This is the call:

          case typrec # case statement
example.
             when "TR001"
                 cntr = test_meth1
                 puts cntr # Here I want to print the counter value.
             when "AB001"
                ab001 += 1
             when "AI001"
                ai001 += 1
             else
                puts "Invalid message type"
          end

I assume that there's a really simple mistake I'm making, so any help
would be greatly appreciated.

You never initialize the 'counter' variable so it's default value is nil. Ruby is telling you that there is no "+" method for a nil object, that is, you can't add 1 to nil.

If "test_meth1" were in a class, you could make counter be an instance variable and initialize it in the initialize method. Since it's not, it'll have to be a global variable. Global variable names start with $.

$counter = 0
def test
   $counter = $counter + 1
   return $counter
end

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3

Tim Hunter wrote:

Peter Vanderhaden wrote:

  from P:/PETERV2/scripts/vlog2.rb:7:in `open'
          case typrec # case statement
          end

I assume that there's a really simple mistake I'm making, so any help
would be greatly appreciated.

You never initialize the 'counter' variable so it's default value is
nil. Ruby is telling you that there is no "+" method for a nil object,
that is, you can't add 1 to nil.

If "test_meth1" were in a class, you could make counter be an instance
variable and initialize it in the initialize method. Since it's not,
it'll have to be a global variable. Global variable names start with $.

$counter = 0
def test
   $counter = $counter + 1
   return $counter
end

Tim,
Thanks very much for the response! I've got it working now.
Peter V.

···

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