Q2-LG03-Selection-Structure-If

Overview of Logical Control Structures in C++

• Subject: CS2 - Introduction to Computational Thinking

• Module Code: 4.0

• Lesson Code: 4.2.1.1 - Selection Structure (If)

• Time Frame: 30 minutes

Learning Objective

• Understand Boolean operations and their application in branching structures.

• Construct selection structure programs to solve specific tasks.

Introduction to Control Structures

• Programs execute statements sequentially in their physical order until completion.

• A need arises to change execution order based on conditions (input validation).

• This requires the ability to ask questions and decide on next actions based on answers.

The Selection Control Structure

• Definition: The selection or branching control structure allows the program to execute statements based on conditions.

  • If a condition is true, execute one statement.

  • If false, execute another or none.

Types of Selection Structures

1. One-way (Single) Selection: Executes one block if the condition is true.

2. Two-way (Double) Selection: Executes one block if true, another if false (if/else).

3. Multi-selection (Compound Block): Uses a switch statement to handle multiple choices.

Selection in C++

• IF Statement: Executes actions based on a condition:

  • Structure: if (condition) statement;

  • If the condition is true, execute the statement; otherwise, proceed to the next.

• IF/ELSE Statement: Chooses between two actions:

  • Structure: if (condition) { statement1; } else { statement2; }

• SWITCH Statement: Chooses actions based on an integer value; supports multiple selections.

Decision-Making in Programming

• Conditions and Questions: In C++, questions are framed as conditions.

  • Example: Instead of asking "Are we having mass testing?", say, "We are having mass testing".

  • A true condition affirms the question (yes); false denies it (no).

Logical Expressions

• Conditions are expressed as logical expressions that evaluate to true or false.

• Forms include:

  • Boolean variables/constants.

  • Variables/values with relational operators (e.g., x > 5).

  • Logical expressions combined with logical operators (e.g., (y < 10) && (b > 2)).

Relational Operators

• Essential for selection control; meanings include:

  • ==: Equal to

  • !=: Not equal to

  • >: Greater than

  • <: Less than

  • >=: Greater than or equal to

  • <=: Less than or equal to

The IF Statement

• Basic structure:

  if (boolean_expression) statement;

• For compound statements (multiple lines):

  if (boolean_expression) {
      statement1;
      statement2;
  }

• Real-life examples of IF statements to illustrate condition-based actions:

  • If it is hot outside, bring an umbrella.

  • If you are thirsty, drink something.

  • If the storm signal is #2, no classes.

  • If your gas is empty, fill up.

Example of IF Statement in C++ Programming

• Example 1: Calculating average scores.

  #include <iostream>
  using namespace std;
  int main() {
      int grade1, grade2, grade3;
      double average;
      cout << "Input 3 scores: ";
      cin >> grade1 >> grade2 >> grade3;
      average = (grade1 + grade2 + grade3) / 3;
      if (average > 60) {
          cout << "PASSED";
      }
  }

  • Sample output: "PASSED" for average score >= 60.

• Example 2: Positive integer check.

  #include <iostream>
  using namespace std;
  int main() {
      int number;
      cout << "Enter an integer: ";
      cin >> number;
      if (number > 0) {
          cout << "You entered a positive integer: " << number << endl;
      }
      cout << "This statement is always executed.";
      return 0;
  }

  • Sample outputs illustrate behavior for both positive and negative inputs.

Conclusion

• The C++ selection control structure is crucial for executing code conditionally based on user input or other criteria.

  • Comprises one-way (IF), two-way (IF-ELSE), and multi-way (switch) options.

  • Encourages logical thinking similar to human decision-making processes.