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Cs 50

This document provides an overview of CS50 weeks 0 through 3. Week 0 introduces binary representation using 0s and 1s, how transistors represent bits, and ASCII encoding of characters. Week 1 discusses C programming basics like main functions, compilers, and input/output functions. Week 2 covers security, cryptography basics like secret key encryption, and string representation in binary. Week 3 is not summarized.

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154 views5 pages

Cs 50

This document provides an overview of CS50 weeks 0 through 3. Week 0 introduces binary representation using 0s and 1s, how transistors represent bits, and ASCII encoding of characters. Week 1 discusses C programming basics like main functions, compilers, and input/output functions. Week 2 covers security, cryptography basics like secret key encryption, and string representation in binary. Week 3 is not summarized.

Uploaded by

bob
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as DOCX, PDF, TXT or read online on Scribd
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EDX- CS50-

WEEK 0
Binary-
0, 1.

To represent 1 in boundary:

4 2 1
1 1 1

= 4+ 2+ 1= 7

Binary digit= BIT

No power = 0
Power = 1

Transistors- act as switches that turn on or off representing 0 and 1s.

To represent 42:
128 64 32 16 8 4 2 1
1 1 1

Similarly ASCII: uses patterns of 0,1 to represent letters.


Eg. 72 73 33: H I !

RGB: represents colours


Eg. 72, 73, 33:

WEEK 1
C programming:
comparing Scratch vs. C

Say = printf
Hello, world= (hello world)

1
Int main(void)
{
Printf(hello world)
}

Main is the default program that is run

Source code -> compiler -> machine code (0100101010)

CS50.io (in the world of Linux)


The compiler is called Clang

$Ls lists the files in the directory


$ rm removes files
$ make- makes a program- and creates a sourcefile in .c format.

$./.<programs name>

$cd change directory


$mkdir- make directory
$rmdir- removes directory

get_char
get_double
get_float
get_int
get_long_long
get_string

%s works as a place holder


String name= get_string()
Printf(hello %s/n, name)

%s strings
%f- floats
\r carriage return
\t- tabs
\
\
\a
\0

2
If
Else
Switch
For
While
Dowhile

In c :
Need to use single quotes- for one character.
Eg if(c==y)

When you define a function and the function does not take any variables you need
to include void into its declaration:
Eg. void cough(void)

Every time we compile a program we do:


-pre-processing: anything with #, is a pre-process directive
-compiling: going from source code to assembly code.
-assembling
-linking.

WEEK 2
Security and Crytography

Cntrl+L- clears the command window

Software critera-
Scope
Correctness
Design
Style aesthetics, readability.

Secret key cryptography

In: key, plaintext


Output: cipher text

String: sequence of characters


Zamyla

Type casting

can convert chars to ints, or ints to chars.

3
String= 32 bits:
\0= 00000000 (8x0 bits in a row)
Nul terminated

Z A M Y L A /0 A
L E X /0

Int main(void)

Int main(int argc, string argv[])

WEEK 3

WEEK 4

WEEK 5

WEEK 6

WEEK 7

WEEK 8

WEEK 9

4
WEEK 10

WEEK 11

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