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Engineering LibreTexts

1.5: Flowcharts

  • Page ID
    10601
  • Overview

    A flowchart is a type of diagram that represents an algorithm, workflow or process. The flowchart shows the steps as boxes of various kinds, and their order by connecting the boxes with arrows. This diagrammatic representation illustrates a solution model to a given problem. Flowcharts are used in analyzing, designing, documenting or managing a process or program in various fields.[1]

    Discussion

    Common flowcharting symbols and examples follow. When first reading this section, focus on the simple symbols and examples. Return to this section in later chapters to review the advanced symbols and examples.

    Simple Flowcharting Symbols

    Terminal

    The rounded rectangles, or terminal points, indicate the flowchart’s starting and ending points.

    graphics1-1.jpg

    Flow Lines

    Note: The default flow is left to right and top to bottom (the same way you read English). To save time arrowheads are often only drawn when the flow lines go contrary the normal.

    graphics9.jpg

    Input/Output

    The parallelograms designate input or output operations.

    graphics3.jpg

    Process

    The rectangle depicts a process such as a mathematical computation, or a variable assignment.

    graphics2.jpg

    Decision

    The diamond is used to represent the true/false statement being tested in a decision symbol.

    graphics6.jpg

    Advanced Flowcharting Symbols

    Module Call

    A program module is represented in a flowchart by rectangle with some lines to distinguish it from process symbol. Often programmers will make a distinction between program control and specific task modules as shown below.

    Local module: usually a program control function.

    graphics7.jpg

    Library module: usually a specific task function.

    graphics8.jpg

    Connectors

    Sometimes a flowchart is broken into two or more smaller flowcharts. This is usually done when a flowchart does not fit on a single page, or must be divided into sections. A connector symbol, which is a small circle with a letter or number inside it, allows you to connect two flowcharts on the same page. A connector symbol that looks like a pocket on a shirt, allows you to connect to a flowchart on a different page.

    On-Page Connector

    graphics4.jpg

    Off-Page Connector

    graphics5.jpg

    Simple Examples

    We will demonstrate various flowcharting items by showing the flowchart for some pseudocode.

    Functions

    pseudocode: Function with no parameter passing

    Function clear monitor
        Pass In: nothing
        Direct the operating system to clear the monitor
        Pass Out: nothing
    End function
    graphics10.jpg
    Function clear monitor

    pseudocode: Function main calling the clear monitor function

    Function main
        Pass In: nothing
        Doing some lines of code
        Call: clear monitor
        Doing some lines of code
        Pass Out: value zero to the operating system
    End function
    graphics11.jpg
    Function main

    Sequence Control Structures

    The next item is pseudocode for a simple temperature conversion program. This demonstrates the use of both the on-page and off-page connectors. It also illustrates the sequence control structure where nothing unusual happens. Just do one instruction after another in the sequence listed.

    pseudocode: Sequence control structure

    Filename: Solution_Lab_04_Pseudocode.txt
    Purpose:  Convert Temperature from Fahrenheit to Celsius
    Author:   Ken Busbee; © 2008 Kenneth Leroy Busbee
    Date:     Dec 24, 2008
    
    Pseudocode = IPO Outline
    
    input
        display a message asking user for the temperature in Fahrenheit
        get the temperature from the keyboard
    
    processing
        calculate the Celsius by subtracting 32 from the Fahrenheit
        temperature then multiply the result by 5 then
        divide the result by 9. Round up or down to the whole number.
        HINT: Use 32.0 when subtracting to ensure floating-point accuracy.
    
    output
        display the celsius with an appropriate message
        pause so the user can see the answer 
    graphics12.jpg
    Sequence control structure
    graphics13.jpg
    Sequence control structured continued

    Advanced Examples

    Selection Control Structures

    pseudocode: If then Else

    If age > 17
        Display a message indicating you can vote.
    Else
        Display a message indicating you can't vote.
    Endif
    graphics14.jpg
    If then Else control structure

    pseudocode: Case

    Case of age
        0 to 17   Display "You can't vote."
        18 to 64  Display "You are in your working years."
        65 +      Display "You should be retired."
    End case
    graphics15.jpg
    Case control structure

    Iteration (Repetition) Control Structures

    pseudocode: While

    count assigned zero
    While count < 5
        Display "I love computers!"
        Increment count
    End while
    graphics16.jpg
    While control structure

    pseudocode: For

    For x starts at 0, x < 5, increment x
        Display "Are we having fun?"
    End for

    The for loop does not have a standard flowcharting method and you will find it done in different ways. The for loop as a counting loop can be flowcharted similar to the while loop as a counting loop.

    graphics17.jpg
    For control structure

    pseudocode: Do While

    count assigned five
    Do
        Display "Blast off is soon!"
        Decrement count
    While count > zero
    graphics18.jpg
    Do While control structure

    pseudocode: Repeat Until

    count assigned five
    Repeat
        Display "Blast off is soon!"
        Decrement count
    Until count < one
    graphics19.jpg
    Repeat Until control structure

    Key Terms

    decision symbol
    A diamond used in flowcharting for asking a question and making a decision.
    flow lines
    Lines (sometimes with arrows) that connect the various flowcharting symbols.
    flowcharting
    A programming design tool that uses graphical elements to visually depict the flow of logic within a function.
    input/output symbol
    A parallelogram used in flowcharting for input/output interactions.
    process symbol
    A rectangle used in flowcharting for normal processes such as assignment.