LAB 4 SELECTION STRUCTURES

Transcription

1 LAB 4 SELECTION STRUCTURES School of Computer and Communication Engineering Universiti Malaysia Perlis 1

2 1. OBJECTIVES: 1.1 Introduction to if, if., nested if and switch statements. 1.2 Able to use selection control structures in programs. 1.3 Able to modify program according to user requirements. 2 INTRODUCTION: In C language, there are several selection methods which can be used: (a) One way selection (b) Two way selection (c) Multi selection (d) Nested if (e) Switch command 2.1 One way selection statement The syntax for one way selection is as below: Compound statement: a group of statements bracketed by { and } that are executed sequentially. { (open curly bracket) and } (close curly bracket) must be used to show the start and end of the commands under the if statement. { Flowchart: ; statement2; start } Yes No 2.2 Two way selection statement The syntax for two way selection is as below: or { ; statement2; } { ; statement2; } 2

3 Flowchart: start statement2 No Yes 2.3 Multi selection statement The syntax for multi selection statement is as below: Flowchart: start F T T F end 2.4 Nested if statement Nested if statement is when one if statement is placed inside another if statement. The nested if statement is used to code decisions with multiple alternatives. The nested if selection can be modified with the use of logic operator (AND) to combine two or more al (relation) statements to be as one statement, thus omits the nested if statement. Nested if Use of logic operator if (() && ()) 3

4 Flowchart: start F T statement2 end 2.5 Switch statement The switch statement is another way to do multi selections statement. The syntax is as follow: switch (variable) { case value1: printf( Message 1 ); break; case value2: printf( Message 2 ); break; case value3: printf( Message 3 ); break; case value4: printf( Message 4 ); break; case value5: printf( Message 5 ); break; default: printf( Default Message ); } Note: The break statement is used to end the switch after the category or selection is selected. Omitting the break statement will not generate a syntax error in your program but it will produce semantic error. Question: Find out what are syntax and semantic errors. 4

5 3 TASKS: 3.1 (a) The following code segment is syntactically correct, but difficult to read. Rewrite the segment using indentation that improves its readability. if (croadstat == 's') if (ftemp > 0) printf("roads wet.\n"); printf("roads icy.\n"); printf("roads dry.\n"); (b) Rewrite the following if statement as an equivalent switch statement. The variable digit is of type int. if (idigit == 0) ivalue = 3; if (idigit == 1) ivalue = 3; if (idigit == 2) ivalue = 6; if (idigit == 3) ivalue = 9; 5

6 (c) The decision table below shows fines imposed for speeding violations. Write a code segment that assigns the correct fine to type double variable fine based on the value of type int variable speed. Speed (mph) Fine ($) 65 or less over (d) Evaluate the expression below assuming a is 5, flag is 1, and c is 15. What part of the expression is not computed at all because of short-circuit evaluation? a!= 3 && flag c >= 10 (e) Write the output for the following code segment. v1 = 15.0; v2 = 0.5; if (v1 > 10.0) printf("ten "); if (v1 > 14.0) printf("fourteen "); if (v2 * v1 > 7.0) printf("seven "); if (v1 - v2 > 9.0) printf("nine "); printf("\n"); 6

7 3.2 Write an interactive program that contains an if statement that may be used to compute the area of square (area = side 2 ) or a triangle (area = ½ x base x height ) after prompting the user to type the first character of the figure names (S or T). a. Write down the flowchart for the program. b. Write your program based on flowchart in (a). 7

8 3.3 Write a program for the National Earthquake Information centre implementing the following decision table to characterize an earthquake based on its Richter scale number. Richter Scale Number (N) Characterization N < 5.0 Little or no damage 5.0 N 5.5 Some damage 5.5 N 6.5 Serious damage: wall may crack or fall 6.5 N 7.5 Disaster: house and buildings may collapse higher Catastrophe: most buildings destroyed a. Write down the flowchart for the program. b. Can you handle this problem with a switch statement? If so, use a switch if not, explain why; c. Write a program based on flowchart in (a). 8

9 3.4 Write a nested if statement for the decision diagrammed in the accompanying flowchart. Use a multiple-alternative if for intermediate decisions where possible. false ph > 7 true ph == 7 true ph < 12 true false Neutral false ph > 2 true Alkaline false Very Alkaline Very Acidic Acidic 9

10 3.5 Write a program that takes the x-y coordinates of a point in the Cartesian plane and displays a message telling either an axis on which the point lies or the quadrant in which it is found. y QII QI x QIII QIV Sample lines of output: (-1.0, -2.5) is in quadrant III (0.0, 4.8) is on the y axis a. Write down the flowchart for the program. b. Write a program based on flowchart in (a). 10

11 3.6 Write a program that assigns to the variable lumens the expected brightness of a standard light bulb whose power has been stored in watts. Use the following table: Power (Watts) Brightness (Lumens) Assign -1 to lumens if the value of watts is not in the table. a. Write down the flowchart for the program. b. Write a switch statement based on flowchart in (a). c. Write a nested if statement equivalent to the switch statement (b) based on flowchart in (a). 11