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What is a switch 🔀

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Notes

Detailed Notes on Switch Statements in C++

What is a Switch Statement?

A switch statement is a control structure in C++ used to compare a single value against multiple possible cases, making it a more efficient and readable alternative to using multiple if-else if statements. It is especially useful when you need to compare a variable to many possible values.

Why Use a Switch Instead of Multiple if-else if Statements?

Using multiple if-else if statements to compare the same variable against many values can be inefficient and hard to read, especially when there are many comparisons. A switch statement simplifies the code and makes it more readable by directly comparing the variable against multiple cases.

Example of Inefficient if-else if Chain:

if (month == 1) {
    // January
} else if (month == 2) {
    // February
} else if (month == 3) {
    // March
}
// Continue for all months

This approach can become difficult to manage and understand when there are numerous comparisons.

Switch Statement Syntax:

The syntax for a switch statement is as follows:

switch (expression) {
    case value1:
        // Code to execute if expression == value1
        break;
    case value2:
        // Code to execute if expression == value2
        break;
    // Additional cases as needed
    default:
        // Code to execute if no case matches
}
  • switch (expression): The expression is the value you’re comparing against multiple possible cases.
  • case value: Each case checks if the expression matches a specific value. If it matches, the code inside that case block is executed.
  • break: After a case block executes, the break statement ensures the program exits the switch statement, preventing the execution of subsequent cases.
  • default: The default case executes when none of the case values match the expression. It is similar to the else statement in an if-else chain.

Example 1: Month Name Based on Input

Here’s an example where we prompt the user for a month number (1-12) and display the corresponding month name:

#include <iostream>
using namespace std;
 
int main() {
    int month;
    cout << "Enter the month number (1-12): ";
    cin >> month;
 
    switch (month) {
        case 1: cout << "It is January"; break;
        case 2: cout << "It is February"; break;
        case 3: cout << "It is March"; break;
        case 4: cout << "It is April"; break;
        case 5: cout << "It is May"; break;
        case 6: cout << "It is June"; break;
        case 7: cout << "It is July"; break;
        case 8: cout << "It is August"; break;
        case 9: cout << "It is September"; break;
        case 10: cout << "It is October"; break;
        case 11: cout << "It is November"; break;
        case 12: cout << "It is December"; break;
        default: cout << "Please enter a number between 1 and 12."; break;
    }
 
    return 0;
}

Explanation:

  • The program asks for the month number.
  • The switch statement checks the month number and displays the corresponding month.
  • The default case handles invalid input (e.g., numbers outside the range 1-12).

Output Examples:

  • Input: 4 → Output: “It is April”
  • Input: 12 → Output: “It is December”
  • Input: -42 → Output: “Please enter a number between 1 and 12.”

Example 2: Letter Grade Based Message

Here’s another example where we use a switch statement to print a message based on the user’s letter grade (A, B, C, D, or F):

#include <iostream>
using namespace std;
 
int main() {
    char grade;
    cout << "Enter your letter grade (A-F): ";
    cin >> grade;
 
    switch (grade) {
        case 'A': cout << "You did great!"; break;
        case 'B': cout << "You did good."; break;
        case 'C': cout << "You did okay."; break;
        case 'D': cout << "You did not do good."; break;
        case 'F': cout << "You failed."; break;
        default: cout << "Please only enter a letter grade A through F."; break;
    }
 
    return 0;
}

Explanation:

  • The program asks for the letter grade.
  • The switch statement checks the grade and prints the corresponding message.
  • The default case handles invalid input (e.g., if the user enters a non-grade letter).

Output Examples:

  • Input: ‘A’ → Output: “You did great!”
  • Input: ‘F’ → Output: “You failed.”
  • Input: ‘Z’ → Output: “Please only enter a letter grade A through F.”

Advantages of Using Switch Statements:

  1. Efficiency: Switch statements are faster than multiple if-else chains when checking for many possible values, because the switch is optimized by the compiler to compare the value directly rather than checking each condition sequentially.
  2. Readability: Switch statements make code easier to read, especially when you have multiple conditions to check.
  3. Simplicity: Instead of writing multiple else if statements, you can condense them into a single switch statement.

Default Case:

The default case is optional but can be very useful. It ensures that if none of the case values match the expression, a message or alternative action is executed. It’s essentially the “catch-all” for unmatched conditions.

Example of Default Case:

In the month example, the default case handles cases where the user inputs a number that is not between 1 and 12. It provides feedback to the user to enter a valid value.

Best Practices:

  1. Order of cases: Switch statements compare the expression against each case from top to bottom. Thus, the order of cases does matter. The first match is executed, and the remaining cases are skipped.
  2. Break statement: Always remember to use break after each case to prevent “fall-through.” Without it, once a case matches, the program will continue to execute the next case’s code, which is often not desired.
  3. Character Comparison: Switch cases can compare characters and integers, but not ranges. Each case must represent a specific value.
  4. Avoid using switch for floating-point values: C++ doesn’t support using switch with float or double types due to precision issues.

Conclusion:

The switch statement is a powerful and efficient control structure in C++ used to compare a single variable against many values. It’s particularly helpful when you have a large number of possible conditions to check, making your code cleaner and easier to manage than using multiple if-else statements. Whether you’re checking months, letter grades, or other values, switch statements simplify your decision-making logic.

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