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Learning Preparation

Techniques for Well Written Code

The main line of the code is clear and uncluttered, with minimal control structures.

Each subroutine focuses on one logical task.

Appropriate use of control structures and data structures.

Correct use of data types to avoid errors.

Comments and stubs are used to aid program maintenance.

Types of Errors

There are 3 main types of errors in code: Syntax, Logic, and Runtime

Syntax Error

Occurs when code doesn’t match syntax os language

Detected on compilation, syntax errors will result in the program being unable to compile

Examples include missing brackets, mispelt/missing keywords, etc.

func syntaxErrorExample {

print("error")

}

// This code would result in a syntax error due to the lack of () at the end of the function name.

Logic Error

Where the algorithm of the code does not produce the required action

Errors detected during testing, when using test data to check the the program works as it should

Code with a logic error will run but not produce the required output

func printUsername() {

var username = "hlewandowski"

print("username")

}

// Result: username

// This code means to print the string in var username, but instead prints the string "username".

// Replacing print("username") with print(username) would fix this issue.

Runtime Error

Occurs while the program is running

Causes the program to terminate or stop, and could be the result of a logic error

Examples include division by zero, overflow, or memory location errors

Error Detection and Correction

A number of tools and techniques can be used to find logic and runtime errors.

Flags

Stubs and Drivers

Debugging output statements

Peer checking

Desk checking

Structured walk through

Comparing actual and expected output

Stubs

Stubs are used to check

The flow or connection between the modules (sub programs) are working

If a subroutine is causing an error by replacing it with a sub (to check if the error disappears, if it does then the error would be in the subroutine)

A section of code, before all sub programs required by that code are finished

// STUB EXAMPLE

REM the following program works out the surface area of a cylinder

DECLARE SUB circ (radius)

DIM SHARED area AS SINGLE

DIM SHARED perimeter AS SINGLE

DIM radius AS SINGLE

INPUT "Please enter the radius of the cylinder"; radius

INPUT "Please enter the length of the cylinder"; length

CALL circ(radius)

surfarea = 2 * area + perimeter * length

PRINT "The surface area is "; surfarea

INPUT "Do you want to do again? (Y/N)"; again$

LOOP UNTIL UCASE$(again$) = "N"

END

SUB circ (radius)

area = 30

perimeter = 10

END SUB

// In the first example above, the sub program “circ” has not yet been complete, so some (arbitrary) values are return from the sub program, so that the rest of the program can be tested (e.g. the surface area formula for a cylinder). “circ" is therefore acting as a stub.

Drivers

A driver is a portion of code that mimics the function of the main line (main program). They are used when the main program is not yet complete and the developers wish to test modules (subroutines). The driver will pass data to the modules and output the returned values. In a sense, a driver is the reverse of a stub.

// DRIVER EXAMPLE

//this is the “add” module that will be tested by the driver

function add(a, b) {

return a + b;

}

//this is the “multiply” module that will be tested by the driver

function multiply(a, b) {

return a * b;

}

//this is the driver that is testing the two modules

function driver() {

const a = 3;

const b = 4;

const sum = add(a, b);

const product = multiply(a, b);

console.log(`sum: ${sum}, product: ${product}`);

}

//calling the driver

driver();

Flags

Flags are used to check that a section of code has been processed or executed. They can be used as part of a solution or as an error detection process. They are normally Boolean variables that change to true (1) if the line of code is executed, e.g. $found = true;

// FLAG EXAMPLE

struct BubbleSortView: View {

@State var sorted = false

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