CSC 130 Class 2

Software Development Lifecycle Rewriting the Problem Statement Three Components of Every Problem Defining Diagram Algorithm Design Tools Flowcharts Starting and Ending Flow Chart Control Structures Sequence Structure in Flow Chart Selection Structure in Flow Chart Repetition Structure in Flow Chart

Analyze a simple problem and develop an algorithm for its solution using various techniques to include top-down development, pseudo code, flow charts, hand-checking, well-chosen test data, and stubs and drivers

Problem Analysis and algorithm development◦ Top down program development◦ Algorithm representation in pseudo code and flowcharts

Step # Step Name Description

1 Requirements Specification Understanding the problem. This will begin by rewriting the problem statement in your own words. If you can’t understand the problem in English you will not be able to solve the problem in a programming language.Discuss the problem with the customers and the users. In this class your instructor is your customer and your user.

2 System Analysis Translate the user and/or customer requirements into technical requirements.Describe input values that are required for the program.Describe the processing that must be accomplished in the program in order to take the input and generate the required output..Describe the outputs that are required for the program.

3 System Design Develop a detailed logical plan to solve the problem that was analyzed in step 2.Break down the problem into small manageable pieces.Use pseudo code, UML, and other appropriate tools to represent your design.Desk check your design using appropriate input data to make sure that the design will give you the correct output.

4 Implementation Translate your design into a programming language. Write the computer program following the syntax of the language. During this phase we will find syntax errors. Syntax errors are “grammar” errors in the programming language.

5 Testing Run your completed program on the computer to make sure that it works. Input real life data and look at the resulting output. You must test all paths through the program.This process is called debugging. You are looking for bugs in your program – bugs are errors. During this phase we will find logical errors. Logical errors are errors with our algorithm – our plan for solving the problem.

The first step for any problem is to fully understand your problem statement. Understand the EXPLICIT details outlined in the problem

◦ These are the facts that you see stated immediately in the problem statement Understand the IMPLIED details required by the problem

◦ These are details that are not stated immediately by the problem statement◦ These are details that are required to support the EXPLICIT details outlined in

the problem. Rewriting the problem statement in your own words helps to define both the

EXPLICIT and IMPLIED details. Details to Consider

◦ What actions the program must be able to do◦ What information the program must be able to remember

If you can’t explain the problem in your own words, then you are not ready to continue with the design process

If you can rewrite the problem in your own words, then you have a good understanding of the problem.

When you rewrite the problem statement, the rewritten version should be longer than the original version.

We own a pizza shop, and we need a better way to control orders and customer records. We’re a small shop, but have lots of part-time workers, and we want to have as much uniformity as possible in how customers and orders are handled. We sell only in the restaurant (no delivery) for both eat-in and carry-out. Regular customers can join the Frequent-Eater’s “club” which entitles them to a free pizza after purchasing 10 pizzas. We sell pizzas with zero or one extra topping (extra cheese, pepperoni, green pepper, mushrooms, or onions). We have two sizes: small and large. If a customer is ordering multiple pizzas, all pizzas must be the same size and have the same topping.

Explicit Details◦ Details that written specifically in the problem statement.◦ Consider action statements from the problem and list them as Action Verb Phrases in the

rewritten problem statement.◦ Consider data details from the problem and list them as information to Remember in the

rewritten problem statement.

Example ◦ Remember the valid pizza sizes of small and large.◦ Remember the number of pizzas in the order◦ Remember the valid pizza toppings of extra cheese, pepperoni, green pepper, mushrooms,

or onions◦ Be able to take an order for a pizza◦ Be able to

Implied Details◦ Details that are not written specifically in the problem statement.◦ Details that are implied based on the problem specifics.◦ Implied details can include both actions and information to remember.

Example ◦ Be able to validate the size of the pizzas in the order (small or large).◦ Be able to validate the number of pizzas in the order (greater than 0).◦ Prompt the user for the number of pizzas in the order◦ Read in the number of pizzas in the order.◦ Remember the number of pizzas in the order

Input◦ A list of source data provided to the problem

Output◦ A list of data generated and provided by the solution to the problem

Processing◦ A list of actions that need to be completed in order to produce the required output for the

problem.

Examples◦ Computer can receive information - Input◦ Computer can print out information – Output◦ Computer can perform Arithmetic – Processing◦ Computer can assign a value to a variable or memory location – Storage◦ Computer can compare two variables and select one of two alternative actions – Processing◦ Computer an repeat a group of actions - Processing

A Defining Diagram is created using the details of the problems statement. A Defining Diagram is created using the explicitly defined details of the problem

and also the implied details of the problem. The Defining Diagram presents the input, output, and processing for the problem in

a simple tabular form. The Defining Diagram does not show time sequence of the problem solution. At this point you do not care how the processing is done – you just need to have a

place holder for the action. Creating the Defining Diagram

◦ Look for descriptive words and nouns – these become the inputs and outputs◦ Look for the actions required and verbs – these become the processing◦ One column for Input, one column for processing, and one column for Output

Example – Adding Two Numbers Problem Statement Create a program that will calculate the sum of two numbers that are entered at the keyboard. The sum

should be printed to the screen.

Defining Diagram

Input Processing Output

first number Prompt for numbers Prompt message for first number

second number Get numbers from keyboard Prompt message for second number

calculate sum sum

Display sum

List of steps involved in accomplish a task. Detailed precise ordered instructions describing the

process necessary to produce the desired output from a given input.

A logic plan for a solution to a problem. We will use the information from the rewritten

problem statement and the Defining Diagram to fill in the details of the algorithm.

Once you understand the problem you are now ready to move forward in the design of the problem. These tools can be used to represent your algorithm (your logical plan to solve the problem) Different design tools work well for different programming languages. Flow Charts

◦ Pictorial representation of the logical steps to solve the problem◦ Flow charts show action and not data◦ Flow Charts are good for procedural programming languages◦ Flow Charts can also be used for defining the steps within a method.

Pseudo code◦ Statements between English and a programming language that represent the logical steps to solve a

problem.◦ Pseudo code can be used to support the design of procedural and object oriented programs◦ Pseudo code can be used to represent both data and action.

UML – Unified Modeling Language◦ This is a design tool used for object oriented programs◦ This can easily show data and action

◦ This can easily show classes, objects, and how they relate and interact with each other.

Pictorial representation of the logical steps it takes to solve a problem. Flow charts show the flow of actions. Flow charts do not show the any information about data Flow charts are not the best tool used to design object oriented programs because they only

show actions and not information Flow charts are good tools for procedural programming languages. Program Steps are placed in different shaped boxes and connected with arrows. These

connections show the order in which the steps must take place. Each shape for a box represents a specific type of action.

◦ Oval for Start and Stop◦ Parallelogram for input and output.◦ Rectangle for processing – for example calculations◦ Diamond is used to ask a question. The question may only have two answers – Yes or No

(true or false) The design for every program begins with Start. The design for every program ends with Stop.

Every flow chart has a starting point The Starting Point is marked with an Oval for Start. Every flow chart has an ending point The Ending Point is marked with an oval for Stop. The actual steps required to accomplish the goals of the program are represented by

other shapes and connecting lines in between the Start and the Stop. 

 

 

 

 

 

 

 

 

   

Start

Stop

Basic shapes represent activities that must occur in the program. Each shape will contain text that specifies details of the activity. Arrows

◦ An arrow always show the flow of actions in a flow chart

◦ The arrow head is always pointing at the next action Rectangle

◦ Shows processing activities such as mathematical calculations

◦ The text inside the rectangle specifies the exact calculation

 

   

 Parallelogram

◦ Shows that input or output of some sort must occur.

◦ Input and output both use the same symbol – the text inside the symbol will differentiate between input and output.

◦ The specific value to input and the source of the input will be specified in the text in the symbol.

◦ The specific value to output and the destination of the output will be specified in the text in the symbol.

   

 

 

   

Calculate Tax based on total sales

Input the student name from the keyboard Output the student name to

the display

Diamond

◦ Shows that a decision must be made

◦ The decision is made based on the answer to a YES/NO question. The only questions that may be asked are YES/NO questions.

◦ One side of the diamond leads to the path of activities that should occur if YES the answer to the question is.

◦ One side of the diamond leads to the path of activities that should occur if NO is the answer to the question.

◦ The text for the question goes inside the diamond

◦ The YES/NO symbols should be written on top of the arrow showing the direction to follow for that answer.

◦ More complicated questions can be made by having a sequence of diamonds.

Is today Wednesday?

YES

NO

Control Structures in programming determine the order of execution of our program statements.

3 Basic Control Structures◦ Sequence◦ Selection◦ Repetition

For now we will discuss Control Structures in terms of flow charts, later we will see how these control structures are represented in pseudo code.

These control structures will be put together in various orders to accomplish the goals of our program.

Statements are executed in sequential order – one after the other. There are no decisions made within a sequence structure This is the default order of execution of programming statements. In a Flow chart sequential structure will show actions flowing one to the other with no

alterative path option. The arrows show the flow of action 

 

 

 

 

 

 

 

 

   

Selection means that a decision is made between alternative paths of execution A question is asked to the computer – a question that has either a yes/no (true/false) answer The answer to the question determines which path of execution is taken. Execution proceeds in either one direction or the other Once the actions have been completed in either the YES or the NO direction, then both paths of execution continue at the same point to complete the

remainder of the sequence of events. A diamond represents a question Arrows will lead from different sides of the diamond showing the optional paths. You must define which direction is yes/true or no/false with a little message

 

 

 

 

 

 

 

 

 

   

Also known as a loop structure A repetition structure allows us to repeat one or more statements in a program multiple times. The statements that we want to repeat are included inside the body of the loop. A decision will need to be made determining when the loop has repeated enough times Again, this is a decision that has a yes/no answer – either you have repeated the loop enough times or you have not. When you have not repeated the loop enough times, execution returns back to the previous steps. When you have repeated the loop enough times, execution continues sequentially forward to other steps. In terms of a flow chart you will need a decision box and arrows that go back to repeat and also to go forward to continue The question that you ask will determine if the YES means to repeat the action or perhaps if the NO means to repeat the action.

 

 

 

 

 

 

 

 

 

   

Problem Statement◦ Create a program that will

calculate the sum of two numbers that are entered at the keyboard. The sum should be printed to the screen

Defining Diagram Input Processing Outputfirst number Prompt for first number Prompt message

for first numbersecond number Read first number from

keyboardPrompt message for second number

  Prompt for second number sum  Read second number from

keyboard 

  calculate sum of two numbers    Display sum  

Software◦ Visio (available free for students through Dreamspark)◦ Raptor – http://www.raptor.martincarlisle.com/◦ Dia -- https://wiki.gnome.org/action/show/Apps/Dia?action=show&redirect=Dia◦ Word – you can insert shapes