CS 115 Chapter 1
Overview of Programming and
Problem Solving
Chapter 1
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Every programmer needs a mental
model of a computer
Every program does: input / process /
output
von Neumann model - the "stored
program" concept
Computer Hardware
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CPU - central processing unit
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Main Memory
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Where decisions are made, computations
are performed, and input/output requests
are delegated
Stores information being processed by the
CPU short-term (volatile)
Secondary Memory (Mass Storage)
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Stores data and programs long-term
Computer Hardware Components
Peripherals
Input Device
Central Processing Unit(CPU)
Control Unit
Arithmetic Logic Unit
Output Device
Auxiliary
Storage
Device
Memory Unit(RAM & Registers)
Memory (RAM)
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a memory cell (also called a word)
has an address, has contents
Contents expressed in bits / bytes binary code
Holds a value which may be data, may
be an instruction
data retrieval = a "copy" not a "cut"
Memory Cells
Address Contents
0
1
2
3
-27.2
354
0.005
-26
4
5
6
H
RTV 001
...
...
999
X
75.62
Secondary Storage
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files - source files, data file, output file
hard disk, floppy, CD, flash memory
stick
slower than RAM, and cheaper per byte
usually much larger capacity than RAM
Units of capacity - Kilobyte, Megabyte,
Gigabyte, Terabyte
Languages
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Machine languages
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Assembly languages
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take a step, lift arm, grasp knob, turn
knob...
LEAVE through DOOR
High-level languages
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"get outta here!"
Programming Languages
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Machine Language
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Most fundamental language of the
computer, the one the CPU "understands"
Unique for each processor type, so not
"portable"
Binary 0s and 1s that specify what to do
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0010 0000 0000 0100
1000 0000 0000 0101
0011 0000 0000 0110
A Program in Machine and Assembly Language
High Level Languages
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Are portable
Programmer writes program in language
similar to natural language (human)
Examples -- FORTRAN, COBOL, Pascal,
Ada, Modula-2, C++, Java
Most are standardized by ISO/ANSI to
provide an official description of the
language
Software Development
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Analyze and specify the problem
Design the algorithm
Implement in code
Testing
Maintenance
Software Development
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Problem Analysis
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Identify data objects
Determine Input / Output data
Constraints on the problem
Design
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Decompose into smaller problems
Top-down design (divide and conquer)
Develop Algorithm (Desk check)
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Algorithm refinement (Pseudocode)
Software Development Method
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Implementation
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Testing
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Converting the algorithm into programming
language
Verify the program meets requirements
System and Unit tests
Maintenance
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All programs undergo change over time
A Tempting Shortcut?
DEBUG
REVISE
REVISE
DEBUG
DEBUG
REVISE
CODE
GOAL
TEST
THINKING
CODE
Translators and Tools
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Assemblers for assembly languages
Compilers for high-level languages
IDE (integrated development environment)
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compiler
editor (creates text format files)
linker
loader
debugger
Translation
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Syntax - the rules governing the
formation of statements in the language
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Spelling
Order of words, statements
Punctuation
Semantics – meaning of the statement
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What does it DO? What action does the
computer do when the statement is
executed?
Processing a Program
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Editor used to enter the program
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Compiler translates the source program
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Displays syntax errors
Creates (usually) temporary object code
Linker to combine object file with other
object files (like library code)
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Creates source program file
Creates final executable program (.exe)
Loader copies exe file into RAM to be
run by machine
Three C++ Program Stages
myprog.cpp
SOURCE
myprog.obj
OBJECT
written in
C++
via compiler
myprog.exe
EXECUTABLE
written in
machine
language
written in
machine
language
via linker
other code
from libraries,
etc.
Ethics
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Responsibility comes with knowledge
hacking
piracy
data theft and data privacy
Responsibility to develop programs
without errors
Some C++ History
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1972 : Dennis Ritchie at Bell Labs designs C
and 90% of UNIX is then written in C
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Late 70’s : OOP becomes popular
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Bjarne Stroustrup at Bell Labs adds features
to C to form “C with Classes”
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1983 : Name C++ first used
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1998 : ISO/ANSI standardization of C++
Objects in a hierarchy
Some C++ History
Dennis Ritchie
Bjarne Stroustrup
Problem Solving Techniques
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Ask questions -- about the data, the
process, the output, error conditions
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Look for familiar things -- certain
situations arise again and again
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Solve by analogy -- it may give you a
place to start
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Use means-ends analysis -- determine the
I/O and then work out the details
More Problem Solving Techniques
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Divide and conquer -- break up large
problems into manageable units
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Building-block approach -- can you solve
small pieces of the problem?
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Merge solutions -- instead of joining
them end to end to avoid duplicate steps
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Overcome mental block -- by rewriting
the problem in your own words
Case Study: Converting Miles
to Kilometers
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Problem Your summer surveying job
requires you to study some maps that give
distances in kilometers and some that use
miles. You and your coworkers prefer to
deal in metric measurements. Write a
program that performs the necessary
conversion.
Case Study
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Analysis The first step in solving this
problem is to determine what you are
asked to do. You must convert from one
system of measurement to another, but are
you supposed to convert from kilometers
to miles, or vice versa? The problem states
that you prefer to deal in metric
measurements, so you must convert
distance measurements in miles to
kilometers.
Data Requirements
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Problem Input
miles
distance in miles
Problem Output
kms
the distance in kilometers
Relevant Formula
1 mile = 1.609 kilometers
Design an Algorithm that solves the
problem
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Algorithm (Pseudocode)
1. Get the distance in miles.
2. Convert the distance to kilometers.
3. Display the distance in kilometers.
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Algorithm Refinement
2.1 The distance in kilometers is 1.609
times the distance in miles
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Desk check!
Miles to kilometers Implementation
Testing
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Test with input data for which you can
easily determine the expected results
E.g.
10 miles should convert to 16.09
kilometers