Ch. 13~15 – Basic Programming Concepts
Supplementary Notes
Problem Solving Procedures (Ch.13)
 Systematic ways of solving problems (p.82)


“Systematic”: Developing step-by-step procedures to solve a problem
“Divide-and-Conquer” strategy
 Break down a problems into smaller sub-problems to solve (modular approach)
 Increase the chance of finding the best solution, as it is easier to solve smaller
problems
 Easier to trace mistakes (narrow down error into a module)
 Six steps (pp.84-92)
 Problem Identification: To precisely define a problem.
 Problem Analysis:


 Identify given input (data) and expected output (result) of a problem
 Identify required processing steps
Algorithm Design:
 Algorithm: procedures to solve the problem
 Algorithm is represented by flowchart or pseudo-code (See. Ch.15 for details)
Developing a Solution (Implementation):
 Top-down approach: Breaking down a problem into sub-problems (modules) and
solve them. (Stepwise refinement)
 Bottom-up approach: Putting together smaller systems to form a bigger system.
(the beginnings are small but eventually grow in complexity and completeness.)
Ref: http://en.wikipedia.org/wiki/Top-down_and_bottom-up_design


Testing and Debugging:
 Testing:
 To make sure that a program operates as it is designed.
 Test cases (test data) are required to ensure a program works without errors.
 General test cases (Entering valid data / Normal use)
 Extreme test cases (Entering invalid data intentionally / Entering data that
may causes problem)
 Debugging:
 To fix errors found in a program.
 Three common types of errors: syntax error, runtime error and logical error.
Documentation:
 User manual = User guide (e.g. how to install and use the program)
 Program manual = Technical details of the program
 Requirement specifications of the problem to solve
 Flowchart or pseudo-code: Describe the algorithm used in the program
 Required inputs and expected outputs of the program
 Source program (source code) listing
 Comment in the program: For other programmers to understand the program
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Ch. 13~15 – Basic Programming Concepts
Supplementary Notes
Common Types of Errors (p.88)
Type
Syntax Error
Description Some program statement not in
correct syntax (grammar rule)
Example  Missing punctuation;
 Misspelling keywords or
commands;
 Incorrect order of
commands.
Discover Error discovered by compiler
Error
(see Ch.14)
Ease of Easy
Debug (Line numbers of problematic
statements are given)
Remark Debugging tool (i.e. debugger)
can help.
Runtime Error
Error encountered during
runtime.
 Division by zero;
 Reading an inexistent file.
 Insufficient system
resources (e.g. memory)
Logical Error
Improper use of control
structure (See Ch.15).
 The program gives
always/sometimes wrong
results.
Error discovered by testing the
program
Difficult
(By tracing the program)
Error discovered by testing the
program
Very Difficult
(By tracing the program or
reviewing the algorithm)
Debugger can help us trace the Debugger can help us trace the
program.
program.
Programming Languages (Ch.14)
 A programming language is an artificial language designed to express computations that can be
performed by a machine, particularly a computer.
Ref: http://en.wikipedia.org/wiki/Programming_Languages
 After an algorithm is designed, we develop (implement) the solution by writing computer
programs, which instruct the computers to carry out suitable operations.
 Low-level VS High-level (programming languages)
Low-level Programming Languages
Feature
Direct instructions to CPU
(In binary data or op-code/mnemonic)
Comparison Disadvantages
- Machine dependent = Not portable = Not
cross-platform
(depending on the instruction set of the
type of CPU)
- Program code is long
- Difficult to learn, understand, write,
debug, maintain, etc.
Example
High-level Programming Languages
More English-like
(Closer to human language)
Advantages
- Machine independent = Portable =
Cross-platform
- Program code is shorter
(because one statement may be translated
to multiple machine instructions)
- Easier to learn, understand, write, debug,
maintain, etc.
Advantages
- Programs are more efficient (run faster)
(direct instructions to CPU, I/O ports or
hardware devices)
Disadvantages
- Programs are less efficient (less fast)
(translated machine instructions have to
be optimized by compiler)
First Generation: Machine Language
Second Generation: Assembly Language
Third Generation: C, Pascal, C++, Java, etc.
Fourth Generation: SQL
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Ch. 13~15 – Basic Programming Concepts
Supplementary Notes
 Programming Languages (pp.109-111)
 First Generation (1GL): Machine Language


 Machines instructions in binary code
 Directly instructs the CPU to work
Second Generation (2GL): Assembly Language
 Using op-code/mnemonic to represent machine instructions
 One instruction in assembly language corresponds to one machine instruction
 Translator (assembler) is required to translate source code (in assembly language)
into object program (machine language)
Third Generation (3GL): Procedural Language
 For general purpose
 Statements as procedures to tell the computer what to do
 Translator (compiler) is required to translate source code into object program
 Fourth Generation (4GL): Declarative Language
 For specific purpose
 Oriented toward problem solving
 Example: Structured Query Language (SQL) – An SQL statement generates results
based on given conditions and required output format
 Fifth Generation (5GL)? More high-level
Note: from 2GL onwards, source code are (mostly) in plaintext and can be edited by text editor
 Translators (pp.112-114)
 They are software tools
 Assembler (see “Assembly Language” above)
 Complier:
 Convert high-level language program (source program) into object program (e.g.
executable file, written in machine language)
 After the object program is generated, the source program and compiler are not
longer required for execution
 The compiler checks for syntax errors, and tell the programmer which lines may
contain errors. It CANNOT check runtime errors and logical errors.

 An Integrated Development Environment (IDE) contain both editor and compiler.
Interpreter:
 There are interpreters for high-level and low-level languages
 The interpreter reads a statement from the source code, translates it into machine
instructions, and then executes them immediately.
 No object program is generated! (No compilation)
 The source program and the interpreter are required for execution.
 Execution is less efficient for complicated tasks, because it involves runtime
translation of program statements. However, it’s easier to trace a program.
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Ch. 13~15 – Basic Programming Concepts
Supplementary Notes
Using High-level Programming Language (Ch.15)
 Variable represents a memory location which stores a piece of data.
 Basic statements (pp.124-126)
 Input statement obtains input from user and stores it in a variable.
 Output statement gives output to user (e.g. on screen).
 Assignment statement assigns a value (or the result of an expression) to a variable. Note
that the variable being assigned must be written on the left hand side.
Example Statement
Input A
Input 3
Output "Hello!"
Output X
Output 3
A = B + 3
A = A + 1
X + 3 = Y
3 = K
Meaning
Ask user for input and store the value in A
Syntax Error! 3 is a number but not a variable
Output a piece of text “Hello!”
Output the value of the variable X
Output the number 3
Calculate B+3 and store the result in A
Add 1 to A and store the result in A
Syntax Error! Left hand side must be a variable to store result
Syntax Error! Left hand side must be a variable to store result
 Control structure (or control flow) refers to the order in which statements are executed.
 Sequence: Statements are executed one by one
 Selection / Choice (pp.129-130): A conditional statement performs different operations
based on whether a condition is true or false.

If-Then: If a condition is true, the then-part is executed.


If-Then-Else: If a condition is true, the then-part is executed, or else the else-part is
executed.
Iteration / Loop (pp.131-135):
 A loop is a sequence of statements which is specified once but which may be carried
out several times in succession.


Infinite Loop
If the condition of
a loop is logically
wrong, it may lead
to “infinite loop” the program cannot
escape from the
loop
Count-control loop (For loop): The loop is repeated for a certain number of times.
Condition-controlled loop:
 While loop: It is a pre-test loop. A condition (“entry condition”) is checked
before executing the loop body. If the condition is false at first, the loop body
is completely skipped.

Do-while loop: It is a post-test loop. A condition is checked after executing
the loop body once. If the condition is true, the loop body is repeated again.

Repeat-until loop: It is also a post-test loop. However, the condition is an
“exit condition” because the loop stops if it is true.
 Tracing program:

Dry run refers to a testing process by tracing a program manually (or running the
program mentally / in mind).

Echo checking refers to the technique of outputting intermediate results on the screen for
checking the logic of a program.
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