Selection Structures - SWITCH Statement - Gateway 选择结构开关语句网关.pptVIP

Switch Case Structures Lecture 9 Switch Multiple Selection Structure A multiple selection structure is useful when an algorithm contains a series of decisions in which a variable or expression is tested separately for one of several possible integral values. Each integral value represents a different action to be taken in the algorithm. C provides the switch multiple selection structure to implement this type of decision making. Switch-Case Structures The switch - case syntax is: switch (integer expression test value) { case case _1_fixed_value : action(s) ; case case_2_fixed_value : action(s) ; default : action(s) ; } Switch-Case Structures The switch is the controlling expression Can only be used with constant integer expressions. Remember, a single character is a small positive integer. The expression appears in ( ) The case is a label The label must be followed by a : Braces, { }, not required around statements Switch-Case Structures Unlike if-else if-else structures, when the value in a case matches the test value, all of the actions in the rest of the structure take place. This is shown in the following program where the user enters a value that matches the first case and every action in the structure is executed. A Sample Program to Illustrate Switch-Case Problem: Write a program to ask the user to enter his/her letter grade and then respond with an appropriate message regarding his/her academic status. A Sample Program to Illustrate Switch-Case Algorithm: 1. Set up the environment 2. Prompt user to enter his/her letter grade 3. Get user’s response 4. If grade is a or A say “Good Job” and go to 9 5. If grade is b or B say “Pretty good” and go to 9 6. If grade is c or C say “Better get to work” and go to 9 7 If grade is d or D say “You are in trouble” and go to 9 8. Say “You are failing” 9. Terminate program A Sample Program to Illustrate Switch-Case /* This program associates a letter grade with a message