Lab 3: Simple Logic Programming

If-else Statements

What are they?

Decision statements such as "if-else" are also called conditionals. They are useful for decision making within a program. For example, if you have to decide if a number is positive or negative you would need an if statement. If it is positive, do one thing, else do another.

How do I use them?

In most programming languages, you can do a simple if statement, an if-else statement, or a series of if-else statements.

1. A basic if statement would look like this:
   if(num >= 0):
   
   print("non-negative")


2. You can also add an else statement to this if you want to do something whether it is or it isn't true:
   if(num >= 0):
   
   print("non-negative")
else:

print("negative")


3. If you have several options, such as wanting to differentiate between 0 and positive numbers in our example:
   if(num > 0):
   
   print ("positive")
elif(num == 0):

print("zero")
else:

print("negative")


4. You can combine two if statements into one using "and" or "or", this is useful if you want to do the same thing for multiple conditions:
   if(num > 0 and num % 2 == 0):
   
   print("positive even number")

If you put two if statements back-to-back without an else or elif it will check both. If you use an elif or else it will only run if the above if statement is false.