PROGRAM-SOLVING AND PROGRAM DESIGN

Transcription

1 PROGRAM-SOLVING AND PROGRAM DESIGN Objective One Outline the steps in problem-solving A problem may be defined as a situation or task that needs to be solved. Problem-Solving is a process which involves finds the most appropriate solution to a specific problem. Computer Programming involves two (2) main phases: (1) he Problem Definition/ Algorithm (2) he Implementation Phases he steps in Problem-Solving (1) Definition of the Problem (2) Propose and evaluate solution (3) Determine the most efficient solution (4) Develop and represent algorithm (5) est and validate solution he Algorithm Phases comprises of the steps in problem solving he Implementation Phases comprises of two (2) steps: (1) ranslate the algorithm (from the algorithm phases) into a programming language such as Pascal, C or C # (2) est the program to make sure it produces the correct results (with the use of trace tables) Objective wo All problems can be decomposed into 4 significant parts. (1) Input (3) Output (2) Processing (4) Storage hus the IPOS chart I P O S I P O S What is given he tasks that must be expected results What is stored (or to performed be) Keywords GE, READ, ACCEP, INPU LE, ASSIGN, SE, SORE PRIN, WRIE, DISPLAY, OUPU name of variable eg X, sum

2 Examples 1: ind the sum of three numbers and display the result. Solution: What is given What Processing is required Expected results What is saved three numbers ind the sum Display the result the sum Solution I P O S Get Num 1 Get Num 1 Print Sum Sum Get Num 2 Get Num 2 Get Num 3 Get Num 3 Let Sum = Num1 + Num2 + Num 3 Print Sum Objective three Distinguish Between Variables and Constants Computers use memory to store data and information. Each of the data items being inputted has to be stored in a location is the computer s memory; it is represented with a label called an IDENIIER. here are two (2) kinds of Identifier: (1) Variables a variable identifies a memory location in which an item of data can be stored i.e; it is an area of storage whose value can be changed during processing. It may be named using capital letters, acronyms Cinclusive of underscore. E.g. X, car id, sum (2) Constants a constant identifies a memory location where a fixed item of data is stored. A constant does not change its value during processing and does not depend on other factors. E.g. Pi ( ), boiling temp. Of water 2, 3. Objective our Use Appropriate Data ypes Data must be given into the computer in a way that it recognizes it. Data type determines the type of data that a variable can store. A data type that treats a variable as a single unit is called an elementary data type. A variable can store any one of the following: Integers: hese are whole numbers, positive or negative without decimal places e.g. -5, 0, 2. loating Point/ Real: hese are positive or negative numbers with decimal values e.g. 0.55, -2.1 Characters: A character is anything that you can key in from a keyboard. his includes letters, numbers and special characters e.g. k,,

3 Objective ive Explain the Concept Of Algorithm An Algorithm is a finite number of accurate, unambigious steps that solve a problem or task. It may also be defined as a sequence of instructions which rigorously defines a solution to a problem. A Program is a set of instructions written in a programming language that directs the computer to solve a problem. Characteristics of an Algorithm A good algorithm should have the following characteristics: A finite number of steps he steps must be precise he steps must be unambigious he steps must have a flow of control from one step to another he steps must terminate thus leading to an output Steps or Developing Algorithms (1) he Input step this is where the instruction from the user are gathered. (2) he Processing step this is where the instructions are worked through. It may involve all or some of the following steps. Assignment values are assigned to variables. Decisoin this step is included when you have to check for any conditions to be followed. Repetition when you have to repeat a task a specified number of times, then this step is included. (3) he Output step - this step is used to display the results. Objective Six Indentifying Ways Of Representing Algorithm Algorithms can be represented in HREE different ways: - (1) Narrative also called General Algorithm, is where each step is written in clear, simple, language. It does not use any comp. lang. or code. (2) Pseudocode a language consisting of English like statements to define algorithms. Even though the terms used closely resemble programming language terms, they are used without following ridig rules. (3) lowcharts a diagrammatic representation of an algorithm Pseudocodes Pseudocodes can contain variables, constants, operators and terminologies used in programming languages. Operators - these are symbols used for performing calculations or making comparisons. Commonly used operators in pseudocodes are:

4 Arithmetic Relational Logical + Addition AND and Substraction OR or NO not Multiplicaion / Division > greater than < less than >= greater than or equal to <= less than or equal to < > not equal to = equal to ruth ables AND OR NO Input Output A B Input Output A B Input Output A Control Structures Control structures are instructions or statements that determine the flow of control of steps in an algorithm. hey are: (1) Sequence instructions are written in the order they should take place. (2) Selection/ Conditional a choice has to be made between two or more options. (3) Interaction/ Repetition/ Looping are used to repeat a certain process a number of times. Repetition of a set of instructions a fixed number of times is called bounded or definite iteration. Repeating a set of steps a number of times until a particular condition becomes false is called unbounded iteration or indefinite iteration. Selection Structure ormat If hen - EndIf If (condition) hen Statements EndIf If hen Else EndIf If (condition) he Statements Else Statements EndIf (true) (false)

5 NB//: he If statement is a conditional statements, that is, it causes execution of some statement to depend on the truth value of a certain statements, given as a Boolean expression. If the condition is RUE, the statements immediately after HEN are executed; if the is ALSE, the statement after ELSE is executed. Bounded/Definite Repetition ormat or Do Endor Set counter variable e.g. = = 0 or (counter variable start value to final value) Do Statements + c accumulator statement Endor Unbounded/Indefinite Loop ormat While Do - End While While (condition) Do statements EndWhile Repeat Unit Repeat Statements to be RUE Until (condition) repeat until Condition becomes RUE lowcharts A lowchart is a graphical representation of the way a computer should progress from one instruction to the next when it performs a task. A flowchart consist of a set of each symbol contains information about what must be done at that point and arrows show the flow of execution of the algorithm. hat is, they show the order in which the instruction must be executed. he six main symbols used in constructing a flowchart are as follows: Name Symbol Description erminator It is used to indicate the beginning and end of an algorithm ( Start/ Stop) Input/output (Parallelogram) Process ( Rectangle) Decision ( Rhombus) Connector It is used to specify an input or output operation e.g. getting data or printing data his is used to specify an operation. E.g. find the average or sum his is used to specify a specify condition. his usually takes the form of a question with possible answers YES or No or rue or ALSE e.g. Is c=0? he arrows leading out of the symbol are labeled YES or NO. he answers lead to the required action corresponding to the answer to the question his is used to a connection point for arrows coming from different directions

6 low line his is used to show flow of instructions ormat for Selection Structure I HEN - ENDI I HEN ELSE ENDI

7 Bounded Structure OR DO - ENDOR Unbounded Structure While Do EndWhile

8 Repeat Until Objective eight esting Algorithms race ables A race able is a tool used for testing the logics of an algorithm for correctness. A trace table is a rectangle array of rows and column; the column heading are the variables in the algorithm. As the instructions in the algorithm are carried out the variables are modified and the changes are recorded in the appropriate column. When the algorithm terminates the final values in the trace table should reflect the correct. Example: Use a trace table to determine the end result of the algorithm using the following data as input 12, 23,34,0. SUM = 0 READ SUM WHILE NUM <> 0 DO ENDWHILE SUM SUM = SUM + NUM READ NUM PRIN he sum of the numbers is, SUM SUM NUM

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