7.5. Omitting the else Clause: Unary Selection

Flowchart of an if with no else

../_images/flowchart_if_only.png

Another form of the if statement is one in which the else clause is omitted entirely. This creates what is sometimes called unary selection. In this case, when the condition evaluates to True, the statements are executed. Otherwise the flow of execution continues to the statement after the body of the if.

 
1
x: int
2
x = 10
3
if x < 0:
4
    print("The negative number " + str(x) + " is not valid here.")
5
print("This is always printed")
6
​

(ch05_unaryselection)

What would be printed if the value of x is negative? Try it.

Check your understanding

select-5-1: What does the following code print?

x: int
x = -10
if x < 0:
    print("The negative number " + str(x) + " is not valid here.")
print("This is always printed")

a.
This is always printed

b.
The negative number -10 is not valid here
This is always printed

c.
The negative number -10 is not valid here





select-5-2: Will the following code cause an error?

x: int
x = -10
if x < 0:
    print("The negative number " + str(x) + " is not valid here.")
else:
    print(str(x + " is a positive number")
else:
    print("This is always printed")



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