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Mastering Control Structures in Programming

Explore switch statement for multiway branching and efficient coding. Learn about do-while loops, for loops, and break/continue statements.

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Mastering Control Structures in Programming

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  1. Chapter 9 More Control Structures

  2. Switch Statement • A multiway branching control structure • An alternative to nested if statements • Uses a switch expression and cases to determine which branch to take • Switch Expression: • The expression whose value determines which switch label is selected. It cannot be a floating-point or a string.

  3. Example switch ( letter ) { case ‘X’: Statement1; break; case ‘L’: case ‘M’: Statement2; break; case ‘S’: Statement3; break; default: Statement4; } Statement5;

  4. Details • The switch statement must be of constant type, i.e., char, short, int, long, bool, or enum. • What comes after the case label must match in type either directly or through coercion to the type of the switch expression. • The default label is optional.

  5. switch vs if switch ( grade ) { case ‘A’: case ‘B’: cout << “Good Work”; break; case ‘C’: cout << “Average Work”; break; case ‘D’: case ‘F’: cout << “Poor Work”; numberInTrouble++; break; }

  6. switch vs if if ( grade == ‘A’ || grade == ‘B’ ) cout << “Good Work”; else if ( grade == ‘C’ ) cout << “Average Work”; else if ( grade == ‘D’ || grade == ‘F’ ) { cout << “Poor Work”; numberInTrouble++; }

  7. Do-While Loop • The do while loop is almost the same as the while loop • The difference is the loop condition is tested at the bottom of the loop • This behavior ensures that the do-while loop is always executed at least once.

  8. Example do { cout << “Enter your age: “; cin >> age; if ( age <= 0 ) cout << “Your age must be positive.\n”; } while ( age <= 0 );

  9. For Loop • The For statement is designed to simply the writing of count controlled loops • You simply take all the pieces you had in a while loop and stick them in the slots in the for loop

  10. Example count = 1; while ( count <= n ) { cout << count << ‘\n’; count++; } for ( count = 1; count <= n; count ++ ) cout << count << ‘\n’;

  11. Break and Continue • The break statement can be used with any loop and switch statements. • If causes the inner most control structure to be exited. • Break can be used to simplify logic, but should be used only as a last resort, not a daily occurrence. • Continue can be used only with loops • It causes the loop to skip to the bottom of the loop iteration and begin a new loop iteration.

  12. Loop Choices • If the loop is a count-controlled loop, the For loop is a natural choice. • If the loop is an event-controlled loop whose body should execute at least once, choose a do-while loop. • If the loop is an event-controlled loop and nothing is known about the first execution, use a while loop • When in doubt, use a while loop. • Pages 453-454.

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