Answers to exercises from Day 1 of learning Lua from "7 More languages in 7 weeks"

lua-exercises-day-1.lua

function ends_in_3(num)
  return string.sub(string.reverse(num), 1, 1) == "3"
end

print("Checking ends_in_3...")
print(ends_in_3(3))
print(ends_in_3(2))
print(ends_in_3(0))

function is_prime(num)
  for i = 2, (num - 1) do
    if ((num % i == 0) and (i ~= num)) then
      return false
    end
  end
    
  return true
end
  
print("Checking primes...")
print(is_prime(0) == true)
print(is_prime(1) == true)
print(is_prime(2) == true)
print(is_prime(3) == true)
print(is_prime(4) == false)
print(is_prime(5) == true)
print(is_prime(13) == true)
print(is_prime(14) == false)

function first_n_primes_ending_in_3(n)
  local number_found = 0
  local current_number = 0 
  
  while (number_found < n) do
    current_number = current_number + 1 
    if (is_prime(current_number) and ends_in_3(current_number)) then
      print(current_number)
      number_found = number_found + 1 
    end
  end

end

print("Printing first_n_primes_ending_in_3...")
-- first_n_primes_ending_in_3(1)
first_n_primes_ending_in_3(10)

function for_loop(a, b, f)
  local i = a
  while (i <= b) do
    f(i)
    i = i + 1
  end 
end

function printer(num)
  print(num)
end

print("Hacking for loop...")
for_loop(1, 5, printer)

function reduce(max, init, f)
  if (max == 0) then
    return init
  end 
  
  return reduce(max - 1, f(init, max), f)
end

function add(previous, next)
  return previous + next
end

print("Reducing addition...")
print(reduce(5, 0, add))

function multiply(a, b)
  return a * b
end

function factorial(num)
  return reduce(num, 1, multiply)
end

print("Factorial...")
print(factorial(8))