Control Structures: Conditional Statements
Conditional statements are fundamental tools in programming that allow you to control the flow of your program based on certain conditions. Let's delve into the details of if, elif, and else statements, which are the building blocks of decision-making in Python.
The if statement
The if statement is the most basic form of a conditional statement. It tests a single condition, and if that condition is true, the code block inside the if statement is executed. If the condition is false, the code block is skipped. This allows your program to make decisions and execute code only when certain criteria are met.
Sample Syntax
if condition:
# Code to execute if the condition is true
Example:
age = 25
if age >= 18:
print("You are an adult.")
In this example, the condition age >= 18 is true, so the message "You are an adult." is printed. If age were less than 18, the code inside the if block would not execute.
The elif statement
The elif statement, short for "else if," is used to test multiple conditions sequentially. You can have multiple elif statements after an if statement. If the initial if condition is false, Python checks each elif condition in order. If one of the elif conditions is true, the associated code block is executed, and the rest are skipped.
Sample Syntax
if condition1:
# Code to execute if condition1 is true
elif condition2:
# Code to execute if condition2 is true
Example:
grade = 85
if grade >= 90:
print("A")
elif grade >= 80:
print("B")
elif grade >= 70:
print("C")
else:
print("D")
In this example, the program checks the value of grade. Since grade is 85, which meets the condition grade >= 80, the program prints "B" and skips the remaining conditions.
The else statement
The else statement provides an alternative code block that executes if none of the preceding conditions are true. It is placed at the end of an if or elif sequence and serves as a catch-all for any conditions not explicitly handled.
Sample Syntax
if condition:
# Code to execute if condition is true
else:
# Code to execute if condition is False
Example
age = 15
if age >= 18:
print("You are an adult.")
else:
print("You are not an adult.")
In this example, since age is 15 and the condition age >= 18 is false, the program executes the code inside the else block and prints "You are not an adult."
Nested if statement
You can also nest conditional statements within each other to create more complex decision-making structures. This allows you to check multiple conditions in a hierarchical manner.
Sample Syntax
if condition1:
if condition2:
# Code to execute if both condition1 and condition2 are true
else:
# Code to execute if condition1 is true but condition2 is false
else:
# Code to execute if condition1 is false
Example:
age = 25
if age >= 18:
if age < 65:
print("You are an adult of working age.")
else:
print("You are a senior citizen.")
else:
print("You are not an adult.")
In this example, since age is 15 and the condition age >= 18 is false, the program executes the code inside the else block and prints "You are not an adult."
Ultimately…
Conditional statements are essential for controlling the flow of a program based on varying conditions. The if, elif, and else statements enable you to create dynamic and responsive code that adapts to different situations. By mastering these statements, you can make your programs more flexible and robust, capable of handling a wide range of scenarios.