1. Computer Programming (CS101) Lecture-02
Asst Prof. Rizwan Khan
Department of Computer & Engineering

2. Introduction to programming

3. What is a program? How to cook? The algorithm Are you a programmer?
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4. Pseudocode This is the pseudocode for a game of Monopoly
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5. Flowcharts
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6. Flowcharts details
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7. Languages Low level (processor dependent) Machine code, assembler
High level: structured, procedural
Fortran, C, Pascal…
High level: object oriented
C++, Java, C#, Perl, Objective-C…
Virtual machines
Java, C#…
Scripting
Perl, Python, JavaScript…
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8. Source code -> Object code
Compiler+linker
Fortran, C, Pascal, C++…
Interpreter
Basic, Perl…
Intermediate
Java
Compiler+linker
Fast to execute, but slow to debug
Interpreter
Slow to execute, but fast to debug (no need to recompile)
Intermediate
Slow…
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9. Source code Instructions Data structures Statement, blocks Affectation
Operators
Loops
Tests
Subroutines
Comments
Data structures
Variable
List
Array
Hash
Pointers
Objects
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10. Source code (2) Statement, blocks Affectation Operator Variable
One or more instructions for the processor
Affectation
Change to a variable
Operator
affect one or more variable
+ * - / AND OR NOT…
Variable
A region in memory that can be modified
Exists in different types
Scalar, char, numeric, boolean
List, array
Hash
Combination->data structure
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11. Source code (3) Pointers Loops Objects Tests Subroutines Comments
Reference to region in memory (address)
Objects
Combination of data and code
Loops
Allow the computer to repeat blocks
Tests
Decide what to do
Subroutines
Programs frequently called (functions)
Comments
The most important lines of the source code…
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12. Number Systems

13. 2-1 INTRODUCTION
A number system defines how a number can be represented using distinct symbols. A number can be represented differently in different systems. For example, the two numbers (2A)16 and (52)8 both refer to the same quantity, (42)10, but their representations are different.
Several number systems have been used in the past and can be categorized into two groups: positional and non-positional systems. Our main goal is to discuss the positional number systems, but we also give examples of non-positional systems.
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14. Common Number Systems System Base Symbols Used by humans?
Used in computers?
Decimal 10
0, 1, … 9
Yes No
Binary 2
0, 1
Octal 8
0, 1, … 7
Hexa- decimal 16
0, 1, … 9,
A, B, … F
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15. Quantities/Counting (1 of 3)
Decimal
Binary
Octal
Hexa- decimal 1 2 10 3 11 4
100 5
101 6
110 7
111
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16. Quantities/Counting (2 of 3)
Decimal
Binary
Octal
Hexa- decimal 8
1000 10 9
1001 11
1010 12 A
1011 13 B
1100 14 C
1101 15 D
1110 16 E
1111 17 F
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17. Quantities/Counting (3 of 3)
Decimal
Binary
Octal
Hexa- decimal 16
10000 20 10 17
10001 21 11 18
10010 22 12 19
10011 23 13
10100 24 14
10101 25 15
10110 26
10111 27
Etc.
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18. Conversion Among Bases
The possibilities:
Decimal
Octal
Binary
Hexadecimal
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19. 2510 = 110012 = 318 = 1916 Quick Example Base Computer Programming
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20. Decimal to Decimal (just for fun)
Octal
Binary
Hexadecimal
Next slide…
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21. Weight 12510 => 5 x 100 = 5 2 x 101 = 20 1 x 102 = 100 125 Base
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22. Binary to Decimal Decimal Octal Binary Hexadecimal
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23. Binary to Decimal Technique
Multiply each bit by 2n, where n is the “weight” of the bit
The weight is the position of the bit, starting from 0 on the right
Add the results
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24. Example
Bit “0”
=> 1 x 20 = x 21 = x 22 = x 23 = x 24 = x 25 = 32
4310
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25. Octal to Decimal Decimal Octal Binary Hexadecimal Computer Programming
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26. Octal to Decimal Technique
Multiply each bit by 8n, where n is the “weight” of the bit
The weight is the position of the bit, starting from 0 on the right
Add the results
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27. Example
7248 => 4 x 80 = x 81 = x 82 =
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28. Hexadecimal to Decimal
Octal
Binary
Hexadecimal
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29. Hexadecimal to Decimal
Technique
Multiply each bit by 16n, where n is the “weight” of the bit
The weight is the position of the bit, starting from 0 on the right
Add the results
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30. Example
ABC16 => C x 160 = 12 x 1 = B x 161 = 11 x 16 = A x 162 = 10 x 256 = 2560
274810
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31. Assignment-02 1.List the differences between Compiler and interpreter.
2.List the differences between low level and high level languages. 3.
Decimal
Binary
Octal
Hexa- decimal
100010
403
2CB
555
1FD
100101
703
11CE
101010
222
1AF
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