Theory of control structures

Transcription

1 Theory of control structures Paper written by Bohm and Jacopini in 1966 proposed that all programs can be written using 3 types of control structures.

2 Theory of control structures sequential structures

3 Theory of control structures conditional structures

4 Theory of control structures repetition structures

5 Control structures in the C language control structures conditional repetition

6 Control structures in the C language decision if / else conditional selection switch

7 Control structures in the C language for repetition iteration recursion do / while while functions

8 Decision with if statement START Display have a nice day IF raining THEN Display reminder to bring umbrella END IF END

9 Decision with if statement

10 Be careful to avoid division by zero in test conditions. When possible, use integer values in test conditions.

11 Decision with if statement START Obtain input number IF multiple of 5 THEN Display message that multiple is found END IF Display remainder of division by 5 END

12 Decision with if statement

13 Decision with if/else statement START Obtain 2 cards IF sum of cards equal to 21 THEN Display blackjack message ELSE Display sum of cards END IF END

14 Decision with if/else statement

15 Decision with if/else statement and logical negation START Obtain 2 cards IF sum of cards not equal to 21 THEN Display sum of cards ELSE Display blackjack message END IF END

16 Decision with if/else statement and logical negation

17 Nested decisions START Obtain 2 cards Calculate sum of cards IF sum of cards is less than 12 THEN IF first card is an ace THEN Add 10 to the sum END IF END IF Display the sum END

18 Nested decisions

19 Nested decisions The decision logic affects the order of the test conditions.

20 Nested decisions It may be possible to optimize the logic of nested decisions.

21 Nested decisions

22 Chained decisions START Obtain 2 cards Calculate sum of cards IF sum of cards is equal to 21 THEN Display the blackjack message ELSE IF 2 cards are actually a pair THEN Suggest that the player split the pair ELSE IF sum is more than 17 THEN Suggest that the player stand the hand END IF END IF END IF Display the sum END

23 Chained decisions

24 Chained decisions The decision logic affects the order of the test conditions. Chained decision structures have only one path of program execution.

25 Selection with switch statement START Obtain 2 cards Calculate sum of cards IF sum of cards is equal to 21 THEN Display the blackjack message END IF IF sum of cards is equal to 21 OR sum of cards is equal to THEN Suggest that the player stand the hand END IF Display the sum END

26 Selection with switch statement

27 Selection with switch statement switch statements must use integer variables. The default selection is always executed. It must be the last selection of the switch statement.

28 Selection with switch statement Selection decision structures may have more than one path of execution. The decision logic affects the order of the comparison conditions. Comparisons are made in sequence from top to bottom.

29 switch statement with break START Obtain 2 cards Calculate sum of cards IF sum of cards is equal to 21 THEN Display the blackjack message END IF IF sum of cards is equal to THEN Suggest that the player stand the hand END IF IF sum of cards is NOT equal to 21 AND sum of cards is NOT equal to THEN Display the sum END IF END

30 switch statement with break

31 switch statement with break The break keyword immediately exits the current switch statement. The default selection is only executed if the switch statement has not ended.

32 Chained decision structures have only one path of execution. Selection decision structures may have more than one path of execution.

33 Use pseudo code and flow charts to design the solution before implementing it with source code. Use extra printf() functions to trace the flow of the program. Check for matching braces when replacing a simple statement with a compound statement.

34 Control structures in the C language control structures conditional repetition

35 Control structures in the C language decision if / else conditional selection switch

36 Control structures in the C language for repetition iteration recursion do / while while functions

37 Iteration using while loops START Initialize sum to zero Initialize counter to zero WHILE counter is less than 3 Obtain input card value Add input to the sum Increase counter by one END WHILE Display sum of all cards END

38 Iteration using while loops

39 Iteration using while loops Watch out for infinite loops!

40 Iteration using while loops The break keyword immediately exits the current while loop. It is possible that the statements inside a while loop is never executed because the test condition was never successful.

41 Iteration using while loops Be careful to avoid division by zero in test conditions.

42 Iteration using for loops START Initialize sum to zero Initialize counter to zero WHILE counter is less than 3 Obtain input card value Add input to the sum Increase counter by one END WHILE Display sum of all cards END

43 Iteration using for loops

44 Iteration using for loops The break keyword immediately exits the current for loop. It is possible that the statements inside a for loop is never executed because the test condition was never successful.

45 Iteration using for loops Be careful to avoid division by zero in test conditions.

46 Iteration using do/while loops START Initialize sum to zero Initialize counter to zero WHILE counter is zero OR counter is less than 3 Obtain input card value Add input to the sum Increase counter by one END WHILE Display sum of all cards END

47 Iteration using do/while loops

48 Iteration using do/while loops The statements inside a do/while loop always execute at least once because the body of the loop executes before it reaches the test condition.

49 Iteration using do/while loops The break keyword immediately exits the current do/while loop. Be careful to avoid division by zero in test conditions.