CS 1
Introduction
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Hardware
1.
2.
3.
4.
5.
Central Processing Unit (CPU)
Main Memory
Secondary Memory / Storage
Input Devices
Output Devices
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Main Memory
• It is volatile. Main memory is erased when
program terminates or computer is turned off
• Also called Random Access Memory (RAM)
• Organized as follows:
– bit: smallest piece of memory. Has values 0 (off, false)
or 1 (on, true)
– byte: 8 consecutive bits. Bytes have addresses.
• Addresses are sequential numbers from 0 to the
maximum amount of memory in your computer.
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Memory Organization
• In the chart above, the number 149 is stored in the
byte with the address 16, and the number 72 is stored
at address 23.
• What these numbers might mean depends upon the
program.
• The concept of the “stored program” computer is this:
that the numbers can be machine instructions.
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Secondary Storage
• Non-volatile: data retained when program is
not running or computer is turned off
• Comes in a variety of media:
– magnetic: floppy disk, hard drive
– optical: CD-ROM, DVD
– Flash drives, connected to the USB port
– Solid-state drives instead of rotating disks
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Machine Instructions
• The C++ compiler translates your program,
which is relatively easy for you to read, into
binary numbers which are the instructions and
data the computer understands.
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Binary (base 2)
• Inside a computer, the contents of memory
cells can be either on or off, or zero or 1.
• Place value: in base 10 you have units, 10s,
100s, 1000s, etc. which are powers of 10.
• In binary: units, 2s, 4s, 8s, 16s, 32s, etc.
Powers of 2 vs. powers of 10.
• Count in binary on your fingers.
• Thus there are 10 kinds of people: those who
understand binary and those who don’t.
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Binary Addition
Add:
0 0 1 1 0 1 0 1
0 0 1 0 1 1 0 1
--------------0 1 1 0 0 0 1 0
Four rules:
0+0=0
1+0=1
1+1=0 carry 1
1+1+1 = 1 carry 1
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Base 8 and Base 16
• It’s easy to convert between base 2 and either
base 8 (octal) or base 16 (hexadecimal) by just
grouping digits.
• Convert 11000111 to hex:
• Groups of 4 because 24 =16
• 1100=1210 = C16; 0111=710
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Base 8 and Base 16
• In base 8, the place values are powers of 8:
Units place, 8s, 64s (82), 512s (83), 4096s (84)
and so on
• In base 16 (hexadecimal) the place values are
units, 16s, 256s (162), 4096s (163) etc.
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Binary to Base 10
Place values:
128 64 32 16
8
0
0
1
1
0
So in the example we have:
0x128=0
0x8=0
1x32=32
1x4=4
0x64=0
0x2=0
1x16=16
1x1=1
4
1
2
0
1
1
Add 32+16+4+1=53
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Elements of a Program
• Common elements in programming
languages:
– Key Words
– Programmer-Defined Identifiers
– Operators
– Punctuation
– Syntax
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Keywords
• Also known as reserved words
• Have a special meaning in C++
• Can not be used for any other purpose
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Identifiers
• Names made up by the programmer
• Not part of the C++ language
• Used to represent various things: variables
(memory locations), functions, etc.
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Operators and Precedence
• Used to perform operations on data
• Many types of operators:
– Arithmetic – * (multiply), / (divide), + (add), (subtract)
– Assignment – ex: = the equal sign
– Comparison: ==
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Punctuation
• Use semicolon to end statements (not every
line is a statement)
• Use comma to separate items in a list.
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Grouping
• Parentheses alter the order of operations in
an expression, and enclose function
arguments.
• Braces {} group statements together.
• Brackets [] are used for array references.
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Language Syntax
• Syntax refers to the way the elements of a
language are put together. For example, in
English the verb form doesn’t usually tell you
the subject, while in Spanish it does.
• Programming language syntax is the way
program statements are constructed.
• Semantics refers to what the statements
“mean.”
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Variables
• A variable is a named storage location in the
computer’s memory for holding a piece of
data.
• The contents can be changed by a program.
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Variable Declaration
• To create a variable in a program you must
write a variable definition (also called a
variable declaration)
• You supply a name and the data type.
• Examples:
– int hours;
– double pay;
– char answer;
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What Programs Do
•
•
•
•
Reduced to simplest terms, a program:
Takes some form of input
Does some processing to it
Creates some kind of output
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Three Basic Constructs
• Execution in sequence
• Making a decision
• Looping
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Creating a Program
1.
2.
3.
4.
5.
6.
Define clearly and precisely what the program is to do.
Use various tools to create a model of the program.
Check your model for errors.
Write code that reflects the model.
Compile the code, which checks for syntax errors.
Correct any errors you find and go back to step 5 if there
are any.
7. Run the program with test data and determine whether
the results are correct.
8. If the results are not what you wanted, make changes and
go back to step 7.
9. Validate the results.
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Two Programming Paradigms
• Procedural programming focuses on the
process. The program generally executes from
start to finish in a linear way.
• Object-oriented programs focus on objects,
which have both data and methods that act
on the data. While an object-oriented
program can be procedural, most respond to
messages from external events.
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