CODEWITHSUNDEEP
rubymethods
user2648884
user2648884

Reputation: 31

How do I create arithmetic statements using variables?

I'm trying to create a method to check if three variables a, b and c are a pythagorean triplet. I set it up with a known triplet: 3, 4, 5. This program won't run though and I can't figure out why.

a = 3
b = 4
c = 5

def triplet?
    if a**2 + b ** 2 == c ** 2
    puts 'pythagorean triplet'
        else puts 'not a pythagorean triplet'
    end
end

triplet?

It returns the error message:

undefined local variable or method `a' for main:Object (NameError)

Any help will be much appreciated.

Upvotes: 1

Views: 53

Answers (3)

Chris Heald
Chris Heald

Reputation: 62648

a, b, and c are local to the scope they're defined in, and thus aren't visible to separate scopes (such as other methods). See the doc on Object#def:

Starts a new local scope; local variables in existence when the def block is entered are not in scope in the block, and local variables created in the block do not survive beyond the block.

What you want to do is pass numbers as parameters: 

def triplet?(a, b, c)
  if a**2 + b ** 2 == c ** 2
  puts 'pythagorean triplet'
    else puts 'not a pythagorean triplet'
  end
end

triplet?(3, 4, 5)

This will define those three variables in the scope of the triplet? method, then you populate their values by passing them when you invoke the method.

A small point of note, by convention, predicate methods (that is, methods ending in ?) in Ruby conventionally return a boolean. To write this method idiomatically, you might say:

def triplet?(a, b, c)
  a**2 + b ** 2 == c ** 2
end

if triplet?(3, 4, 5)
  puts 'pythagorean triplet'
else
  puts 'not a pythagorean triplet'
end

That way, triplet? will always return a boolean true or false, then you can use it in your code to write English-y sentences.

Upvotes: 2

sunnyrjuneja
sunnyrjuneja

Reputation: 6123

a = 3
b = 4
c = 5

def triplet?(a, b, c)
    if a**2 + b ** 2 == c ** 2
        puts 'pythagorean triplet'
    else 
        puts 'not a pythagorean triplet'
    end
end

triplet?(a, b, c)

def creates a function. Inside the function block, you have a scope. a, b, and c are not in that scope. Tell the function to take parameters a, b, c and pass it the parameters.

There is no relation between the name you give the function parameters and the function parameters you pass.

The following will also work:

x = 3
y = 4
z = 5

def triplet?(a, b, c)
    if a**2 + b ** 2 == c ** 2
        puts 'pythagorean triplet'
    else 
        puts 'not a pythagorean triplet'
    end
end

triplet?(x, y, z)

Upvotes: 0

sawa
sawa

Reputation: 168091

Within the definition block, which is the scope for local variables, a is not defined, hence the error message.

Upvotes: 0

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