Understanding Selection Structures
- Selection structures are fundamental programming constructs that allow you to make decisions within your code.
- They enable your program to execute different blocks of code based on specific conditions.
Selection structures are also known as conditional statements or decision-making constructs.
Types of Selection Structures
- If Statements: Executes a block of code if a specified condition is true.
- If-Else Statements: Provides an alternative block of code to execute if the condition is false.
- Else If (Elif) Statements: Allows multiple conditions to be checked in sequence.
- Boolean and Relational Operators: Enhance the flexibility of selection structures by allowing complex conditions.
When designing selection structures, always start by clearly defining the conditions that will guide your program's decisions.
The Role of Selection Structures in Programming
- Selection structures are essential for controlling the flow of a program.
- They enable your code to:
- Respond to User Input
- For example, display different messages based on a user's age.
- Handle Different Scenarios
- For example, determine the next action in a game based on the player's performance.
- Implement Business Logic
- For example, calculate discounts based on purchase amounts.
- Respond to User Input
- Think of selection structures as traffic lights for your program.
- They direct the flow of execution, ensuring that the right actions are taken based on the current conditions.
If Statements: The Building Block of Decision-Making
- If statements are the simplest form of selection structure.
- They execute a block of code only if a specified condition is true.
Syntax and Structure
Python:
if condition:
# code executes if condition is trueJava:
if (condition) {
// code executes if condition is true
}Recommending Activities Based on Age
Python:
age = 16
if age < 18:
print("Recommended activity: Play video games.")Java:
int age = 16;
if (age < 18) {
System.out.println("Recommended activity: Play video games.");
}The condition inside the if statement must evaluate to a Boolean value (true or false).
If-Else Statements: Providing Alternatives
If-else statements extend the basic if structure by providing an alternative block of code to execute if the condition is false.
Python:
if condition:
# code executes if condition is true
else:
# code executes if condition is falseJava:
if condition:
# code executes if condition is true
else:
# code executes if condition is falseRecommending Activities for All Ages
Python:
age = 16
if age < 18:
print("Recommended activity: Play video games.")
else:
print("Recommended activity: Go to the gym.")Java:
int age = 16;
if (age < 18) {
System.out.println("Recommended activity: Play video games.");
} else {
System.out.println("Recommended activity: Go to the gym.");
}Use if-else statements when you need to ensure that one of two possible actions is always taken.
