Control Flow

Conditional branching statements.

age = 18

# Simple if
if age >= 18
  print("Adult")
end

# If-else
score = 75
if score >= 60
  print("Pass")
else
  print("Fail")
end

# Else-if chain
grade = 85
if grade >= 90
  letter = "A"
elsif grade >= 80
  letter = "B"
elsif grade >= 70
  letter = "C"
elsif grade >= 60
  letter = "D"
else
  letter = "F"
end
print(letter);  # "B"

The then keyword is an optional separator between the condition and the body of an if or elsif statement. It improves readability, especially for single-line conditionals.

# Multi-line with then
if age >= 18 then
  print("Adult")
end

# Single-line with then
if user != null then print("Welcome, " + user.name) end

# Works with elsif too
x = 42
if x > 100 then
  print("big")
elsif x > 10 then
  print("medium")
else
  print("small")
end

# Parentheses and then can be combined
if (score >= 90) then
  grade = "A"
end

# Without then (also valid)
if age >= 18
  print("Adult")
end

Note: then is purely syntactic sugar. Both if condition then ... end and if condition ... end are equivalent. Parentheses around the condition are also optional.

Repeats while a condition is true.

i = 0
while i < 5
  print("Count: " + str(i))
  i = i + 1
end
# Output: Count: 0, 1, 2, 3, 4

Iterates over collections or ranges.

# Iterate over array
fruits = ["apple", "banana", "cherry"]
for fruit in fruits
  print(fruit)
end

# Iterate with range
for i in range(0, 5)
  print(i);  # 0, 1, 2, 3, 4
end

# Range with step
for i in range(0, 10, 2)
  print(i);  # 0, 2, 4, 6, 8
end

# Nested loops
for i in range(1, 4)
  for j in range(1, 4)
    print(str(i) + " x " + str(j) + " = " + str(i * j))
  end
end

Ruby-style postfix conditionals for concise one-liners.

x = 10
print("big") if x > 5

y = 3
print("small") unless y > 5

status = "active"
print("Welcome!") if status == "active"
print("Account locked") unless status != "banned"

Inline conditional expression.

x = 10
size = x > 5 ? "large" : "small"
print(size);  # "large"

# Nested ternary
grade = 85
letter = grade >= 90 ? "A"
      : grade >= 80 ? "B"
      : grade >= 70 ? "C"
      : grade >= 60 ? "D"
      : "F"
print(letter);  # "B"

Skips to the next iteration of the loop.

numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
sum = 0
for n in numbers
  if n % 2 == 0
    next
  end
  sum = sum + n
end
print("Sum of odd numbers: " + str(sum));  # 1+3+5+7+9 = 25