(5-1) Selection Structures III in C H&K Chapter 4. Instructor - Andrew S. O Fallon CptS 121 (September 19, 2016) Washington State University

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1 (5-1) Selection Structures III in C H&K Chapter 4 Instructor - Andrew S. O Fallon CptS 121 (September 19, 2016) Washington State University

2 Advantages of switch Statements (1) One issue with nested if statements is readability The deeper the nesting, the more difficult it can be to figure out what's happening Another issue is that the programmer could mistakenly "mis-nest" if statements, as in the previous example found in lecture set 4-3 In cases in which the nesting is based on the value of a single variable, a switch statement may be a better alternative Offer the potential for faster execution through the program 2

3 Advantages of switch Statements (2) Easier to debug Understandability Maintainability 3

4 switch Statements Example (1) Let's revisit the previous baseball scenario: A high school baseball team awards merit points to players based on their offensive performance. A single (encoded 's') is worth 1 point, a double (encoded 'd') is worth 2 points, a triple (encoded 't') is worth 3 points, and a home run (encoded 'h') is worth 4 points. Any at-bat that leads to an out (encoded 'o') worth 0 points. Write a C statement that, given an at-bat character, properly awards points. 4

5 switch Statements Example (2) The switch statement provides a cleaner way to handle this scenario: } char at_bat; int points; points = 0; printf("enter the at-bat code (s,d,t,h,o): "); scanf(" %c",&at_bat); switch (at_bat) { case 's': /* single */ points = points + 1; case 'd': /* double */ points = points + 2; case 't': /* triple */ points = points + 3; case 'h': /* home run */ points = points + 4; case 'o': points = points + 0; default: /* Anything but 's','d','t','h' */ printf("unrecognized at-bat code."); Don't forget the begin and end curly braces Don't forget to end each case with break If at_bat does not match any other case labels, the default case is executed 5

6 switch Statements Example (3) What if we also want to allow capital letter codes? switch (at_bat) { case 's': /* single */ case 'S': points = points + 1; case 'd': /* double */ case 'D': points = points + 2; case 't': /* triple */ case 'T': points = points + 3; case 'h': /* home run */ case 'H': points = points + 4; case 'o': case 'O': points = points + 0; default: /* Anything but 's','d','t','h' */ printf("unrecognized at-bat code."); } A single case can contain an arbitrary number of case labels 6

7 switch Statements Example (4) Let's revisit the following scenario: A high school baseball team awards merit points to players based on their offensive performance and the class standing ('f' = freshman, 'o' = sophomore, 'j' = junior, and 's' = senior). In particular, freshmen and sophomores earn an extra point for home runs, whereas juniors and seniors do not earn any points for singles. Write a C if-statement that, given an at-bat character and a class standing character, properly awards points. 7

8 switch Statements Example (5) We can write this more clearly as a switch statement with embedded if statements : switch (at_bat) { case 's': /* single */ if (class_standing == 'f') (class_standing == 'o') { points = 1; } case 'd': /* double */ points = 2; case 't': /* triple */ points = 3; case 'h': /* home run */ if ((class_standing == 'f') (class_standing == 'o')) { points = 5; } else { points = 4; } case 'o': points = 0; default: /* Anything but 's','d','t','h' */ printf("unrecognized at-bat code."); } 8

9 You Try It (revisited) Consider the following scenario: In an effort to make their weather reports more user-friendly, the national weather service would like to translate relative humidity percentages (integers between 0 and 100) into descriptions as follows: 20% or lower "bone dry" 21% - 40%: "dry" 41% - 60%: "moderately dry" 61% - 80%: "moderately humid" 81% or higher: "humid" Write a switch statement that, given the relative humidity (an int between 0 and 100), prints out the appropriate description. Will this work? Why or why not? 9

10 switch Statements Best Practices Notes on switch statements You cannot switch based on the value of a double or string variable: char code[20] = "home run"; double era = 1.67; switch (code) { /* can't do this */ switch (era) { /* can't do this either */ An arbitrary number of statements can follow a case label It's a good idea always to define a default case A common mistake is to forget to end a case with break. If a break is forgotten, execution "falls" through to the next case label! 10

11 Next Time Repetition in C Executing statements while a condition is true Can eliminate redundant sequential statements 11

12 References J.R. Hanly & E.B. Koffman, Problem Solving and Program Design in C (8 th Ed.), Addison- Wesley, P.J. Deitel & H.M. Deitel, C How to Program (7 th Ed.), Pearson Education, Inc.,

13 Collaborators Chris Hundhausen 13