This post presents some basic commands for control flow, specifcally if-statements, while and for-loops

If-statements

Let’s start with a simple if statement:

if number > 0:
  print("The number is larger than zero.")

Important to note here are two things: The if-clause ends with a colon and the body of the if-statement needs to be indented correctly.

An if-statement can be combined with an else-clause in the following way:

if number > 0:
  print("The number is larger than zero.")
else:
  print("The number is not larger than zero.")

Again, the body belonging to the else branch needs to be indented.
The ternary operator is an alternative for if..else:

number = int(input("Please enter a number: "))
message="The number is larger than zero." if number > 0 else "The number is not larger than zero."
print(message)

.

Another variant is if..elif which allows to handle multiple branches in the flow of our code:

if number > 0:
  print("You entered a positive number.")
elif number < 0:
  print("You entered a negative number.")
else:
  print("You entered zero.")

while-loops

Following is a simple example of a while-loop

userinput = ""
while userinput != "X":
  print("Main menu")
  print("---------")
  print("Create - 1")
  print("View all - 2")
  print("Delete - 3")
  print("Exit - X")
  userinput = input("Enter your choice: ")

for-loops

for-loops can be used in various ways, e.g. for iterating through a string:

word = "hello"
for letter in word:
  print(letter)

The limit of the loop can be defined using the range keyword:

for i in range(10):
  print(i, end=" ")

It is also possible to define the counting interval:

for i in range(0,10,2):
  print(i, end=" ")

Last but not least, a for-loop can be executed backwards:

for i in range(10,0,-1):
  print(i, end=" ")