Chapter 2 Assignment Page
 Simple Sequence Control Structure

NOTE: The understanding of the method the computer uses to solve problems is critical to the rest of the course. When you solve each of the problems in the chapter use the memory diagrams and walk through the steps one at a time as if you are the computer system.

  1. Algorithm – a step-by-step procedure to solve a problem. NOTE: Beginning with this chapter, the you will develop algorithms for the problems in the chapter using either flowcharting.
  2. Characteristics of an algorithm – algorithms must use only operations for a given set of basic operations and produce the problem solution, or answer, in a finite number of such operations. NOTE: the algorithm must only use the three control structures simple sequence, selection and iteration. This chapter focuses on the simple sequence control structure. Chapter 3 covers the selection control structure. Chapters 4 and 5 cover the iteration control structure.
  3. Character, field, record, and file: NOTE: data is input into the computer system in the form of a record. The records are stored in files on a secondary storage device or input by the user. Cover the terms character, field, record and file and then start solving problems listed at the end of the chapter. Gradually add in the other concepts for the chapter as they are needed.

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    Character – A character is a letter, number or special character. A character is any key pressed on the keyboard.

    Field - a single piece of data, or fact, about a single entity in a file. For example, an employee number might be one of the fields in a payroll record. A field is made up of characters.

    Record – a collection of data, or facts about a single entity in the file. A record is made up of fields.

    File - a file is a collection of related data or facts. A file is made up of records.

  4. Function of Random Access Memory in reference to the memory diagrams used in the chapter – when data is input into the computer system it is initially stored in Random Access Memory. If the data is not stored in Random Access Memory, the computer system can not access the data. NOTE: the problems solved in this chapter illustrate the use of memory diagrams. The memory diagrams will show you what data is stored in memory.
  5. Variables, constants and assignment statements - a memory location must be created to store data in memory. The data can either be stored as a variable or a constant.
Variable - A variable stores data items whose values may change, or vary, during processing. Variable names are created to represent these data items. Examples of variables are name, address and social security number. When data is input into the computer system, you will not have an entire file with all names, addresses and social security numbers the same. Therefore, the data is stored in a variable name so that the data values can change.

Example: Read Name, Address, SSN - This statement will cause the computer system to transfer data from an input file into RAM. The data will be stored in the three memory locations created called name, address and SSN.

Constant - a constant is a value that never changes. You can either use the constant directly in the program design or create a variable name to store the constant. An example of a constant is the sales tax. If you are designing a program that uses the sales tax, the amount will not change from one input record to the next.

Example: Sales Tax = 4.5%

Assignment - if additional data is need to solve a program, an assignment statement must be created. An assignment statement must adhere to the following rules of formation:
    1. Only a single variable name may appear to the left of the assignment symbol, which in our example is =.
    2. Only a single variable name, constant, or expression may appear to the right of the =.
    3. Everything to the right of the = must be known (defined) to the computer.
Example: Sale = Price * Sales Tax
    1. Mathematical order of operations – when you are creating assignment statements, you need to use the mathematical order of operations. Computer systems use the same order of operations to solve problems. The math operations are solved in this order. PEMDAS – Parenthesis, Exponents, Multiplication, Division, Addition and Subtraction. Multiplication and Division are on the same level. Addition and Subtraction are on the same level. When the computer deals with operators on the same level, they are processed from left to right. NOTE: Problem #9 on page 34 reviews the order of operations.
Example: (2 + 3) * 6 =
     5 * 6 = 30
    1. The statement in the parenthesis is performed first.
    2. Multiplication is performed last.
The same formula without the parenthesis will give a different result.

2 + 3 * 6 =

2 + 18 = 20
    1. Multiplication is performed first.
    2. Addition is performed last.
    1. General I/O, process, flowlines, and terminal interrupt symbols – NOTE: Use your flowcharting template or flip to Appendix A on page 309 in the Tools for Structured Design textbook to identify the symbols. This section covers the four basic flowcharting symbols used in this chapter. The other symbols will be introduced in future chapters.
Input/Output Symbol – this symbol is used to input data into the computer system and output information from the computer system. When the symbol is used for input, the word READ is placed in the symbol with the variable locations where the data will be stored. When the symbol is used for output, the word WRITE is placed in the symbol with the variable locations that need to be output. The information is output in the order it appears on the WRITE statement.
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Process Symbol – used for any processing step, an operation or group of operations causing change in value, form or location of data. This symbol is used for all assignment statements.

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Flowline Symbol – represent sequence of operations and direction of data flow. Arrowheads are required if linkage is not top-to-bottom or left-to-right. If no arrowheads are list, the direction of data flow is assumed to be top-to-bottom or left-to-right.

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Terminal Interrupt Symbol – this marks the terminal point in a flowchart. It is placed at the beginning and end of each flowchart or flowchart segment.

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 Exercises: In Chapter 2, the lab problems allow you to trace through flowchart designs in the textbook. You will also create your own flowcharts. It is important to be methodical when you cover the solutions to the problems. Although you can not memorize the solution to each problem in the book, you can learn the method to solving the problems. You should first list the input that is given in the problem, second list the output that is needed, compare the output that is needed to the input that is given, if they match then they should cross it off the output list. Any of the variables that are left on the output list require processing statements. Before the solution to the problem is solved, the processing steps need to be placed in the correct order.

Problem #9 - These problems practice the mathematical order of operations.

Problem #10 – With this problem, you will take input data and walk it through a flowchart. Draw an empty box to represent memory. Walk through each step of the flowchart one step at a time, recognize the use of the flowcharting symbol, create the locations for the variables in memory and place the data in the locations. Using this problem, the you will understand how the computer system processes data. The problem uses many mathematical operations. The problem using many mathematical operations. You may need a calculator to solve the mathematical operations.

Problem #11 – This problem is the same as #10. Define the terms variable and constant. Step d requires you to walk through the flowchart using the given input and memory diagrams.

Problem #13 – This is the first full problem the you will design. You need to create variable names. The variable names should be descriptive, but kept to one or two words. Place three columns on a sheet of paper labeled input, output and processing. List the input given and output required. Compare the input and output. The variables left in the output column require processing. At this point, there is no major difference between the flowchart and pseudocode solution.

Problem #15 – In this problem, you need to create five separate locations for each grade to be stored. You also need to use parenthesis to calculate the total first and then divide the total to calculate the average.

Problems #16 & #17 - These problems are difficult since most people do not remember the formulas for perimeter, area and circumference. Once you have completed the input, output and processing columns, if you do not remember the formulas, leave that portion blank. Normally these types of formulas they can look up in a book. You will not need to know these formulas anywhere else in the class.