Bit byte vs word

• Binary digit - bit
  • Holds 0 or 1 on or off true or false
• Byte is 8 bits in 1
• Word could be one or more bytes

Types of Expression

• Every expression has an associated type
• 3+4 = 7, we know they’re ints
• 3 + 4.1 = 7.1
• 3 is an int, and 4.1 is a float
• 3 < 4 = 1 true · Unary operation
• ++cat · Binary
• Cat + dog · In a binary operation, both operands are converted to the dominating type
• Result is dominating type · Automatic typecasting, converts types based on dominance

Forced type conversion

Type casts

· The type of an expression can be temporarily changed with a type cast · Can be constructed with any off the basic types in C · No restrictions on the use of type casts

• Floats do not have precise storage in computers Data may be lost in this process.

Memory buffer and C executable file

· Stdin Memory buffer

• When scanf is runned, it looks inside stdin
• Enter key is \n · C executable
• Pulls in and checks stdin
• Puts out variables to stdout · Stdout
• Memory buffer
• Variables get put here
• Stdout puts out what needs to be displaye*

Bit operations on the ints

· Least significant bit

• The bit in a binary number that is of the lowest numerical value · Most significant bit
• The bit in binary number that is the highest numberical value · 10101100
• 1 is most significant
• 0 least significant · Count right to left, start from 0 · Bitwise negation
• ~
• Flip the bits
• Replaces all the 0 bits by 1 and all of the 1 bits by 0
• Basically a mirror image of binary · Bitwise AND
• & <- one of these
• && is logical operation
• Takes binary, stack them on top of the bits and combine them,
• 1 & 1 is 1 , 1 & 0 is 0, 0 & 1 is 0 , 0 & 0 is 0 · Bitwise OR
• |
• Same thing with logical or but with bits · Bitwise XOR
• ^
• Same logic but with every bit

Bit masks

· Is a number that we can & | ^ · To detect whether or not a certain bit is on or off · To turn a bit on or off · 16 bit numbers to be able to use as flags · 2^(whatever bit) we wanna know is on or off using &

• Result is 0 if off
• Result is 2^(bit) if on ex 64 = 2^6 · XOR can turn off the bits, and can turn it on
• 0 ^ 1 is = 1 1 ^ 0 = 0
• Essentially subtracting but for computers
• Also can turn it on whatever it’s worth, adding · Using non powers of 2, results in adding and subtracting · Can be used to determine if number odd or even
• Check the last bit to determine if odd or even 0 = even, 1 = odd
• 2^0 = 1

Bitshifting

• Shifts left <<
  • 00000001
  • 00000010
  • Used for multiplication
• Shifts right >>
  • 10000000
  • 01000000
  • Used for division

Random Number Generator

• Int rand(void)
  • Gives you a pseudo random number in the range of 0 to RAND_MAX
  • RAND_MAX is a constant
• rand() % 50
  • Gives it a specified range
  • 0 - 49
  • In stdlib.h
• Pseudo random number
  • Pulls from a list of random number
  • Doesnt actually generate random numbers
• srand()
• srand(time(0))
  • Seed rand, seeds the random number generator to start at a different place in the list
  • We pass time(0) since Epoch into this to seed the generator
    • To start in a different set of random numbers
    • Since it changes every second
  • Need to include stdlib.h
  • And time.h
  • For this
  • Srand should be at the top of int main, should not be called more than once or be used in a function
• Random number within a range
  • Dont want it hardcoded, use a special formula
  • How to find random number inclusively between 32 and 87
  • Making the mod (end-start) correct size but not in the right spot in number line
    • rand() % (end-start+1) + start;
    • Used to find a number within the range of what u want
      • rand() % (87-32+1) + 32;
• Random numbers are NOT unique
• For coding assignment 3 we need to come up with these numbers to be unique
• How do you get unique numbers
  • Basically set the formula rand() % (end-start+1) + start and fill it up in an array, asking if the number generator generates something unique and then putting that in said array and keep on asking it within a range

Arrays

• Aggregate type
• Ised to store collections of related data
• Multiple values of the same data type can eb stored with one variable name.
• Ways to initialize array
  • Method 1 the array declaration
    • Comma separated list enclosed in braces
      • Char cat [] = {}
      • NOT reserving space in memory
      • Only can leave it empty if you fille the
• Initialization of arrays out of bounds
  • You can overwrite memory
  • Can lead to seg faults
  • Overflow
• Storing and printing arrays
  • Dont need & for printing %s
• Passing arrays
  • Calling functions
    • Do not use the brackets when passing arrays
    • Passing address of the array with its name
    • Not possible to pass acopy of the array as ta parameter
  • function(array)
  • Void function(int array[])

/* 512 loop* /

#include <stdio.h>
#include <stdint.h>
int main()
{
    uint8_t a = 0;
    uint8_t b = 6;
    int a_equal_b, a_less_than_b, a_greater_than_b;
    printf("a\t a == b\t a < b\t a > b\n");
    for (int i = 0; i < 512; i++)
    {
        printf("%u\t %u\t %u\t %u\n", a, a==b, a<b, a>b);
        a++;
    }
    return 0;
}

/* 32 loop */

#include <stdio.h>
#include <stdint.h>


int main()
{
    uint8_t a = 0;
    uint8_t b = 6;
    int a_equal_b, a_less_than_b, a_greater_than_b;


    printf("a\t a == b\t a < b\t a > b\n");
    for (int i = 0; i < 32; i++)
    {
        printf("%u\t %u\t %u\t %u\n", a, a==b, a<b, a>b);
        a = (a+1) % 16;
    }
   


    return 0;
}

4 bit adding in binary

• 1111 all bits are on 1111=15
• 1001
• Binary addition
  • Pretty much know this
• If you have a 5th bit when adding in 4 bits you overflow
  • Take away 5th number
  • Same thing in 8 bit world

Two’s complement

• How do we represent negative numbers in binary
• Several ways
  • Using sign bit
  • One’s complement
  • Two’s complement
• Two’s complement is the most commonly used technique
• Sign bit
  • Cut the circle in half
  • Positive 5 in binary
  • 0101 = 5
  • If we use the first bit to determine the sign, then negative 5 is
  • 1101 = -5
    • Cant take 5 and -5 to get 0
    • You get 2
• One’s complement
  • Flips all bits,
  • 5 + -5 = -0
  • Inverting all the bits makes the calculation off by 1
• Two’s complement
  • Get an extra negative number -8
  • 5 + -5 = 0
  • Just works
  • Works like how our numbers work
  • Everything lines up great
  • “It just works, it just fuckin works”
• How to calculate it
  • Flip the bits
  • Add 1
  • Thats how you get 2’s compliment
  • 0101
  • 1010 flip
  • 1011 add 1
• Looking at the binary number out of context you cant tell if it’s negative or positive

Functions

• Type
• Name
• Parameters
• Executable inside
  • Parameters
    • What type they are
    • What order they are in
    • How many there are
  • These 3 things make up function signature
  • • the functions name
• Default type for C is type int
  • Any other type must be explicitly declared
• Type must match expression
  • Return cat ~ cat = float return type = float
• Void is used for not returning anything
• Functions aren’t required to return a type
• If a function does return a value do we need to catch it
  • Nope

Function prototypes

• Way to introduce them to the compiler, to let them know what they look like
• Take definition, copy past add ;
• In them variable names dont really matter
• What does compiler do with the prototype
  • Do a lot of things but mainly matches things up
  • Plays a little matching game

Ternary operators

• 3 things
• Ternary if
  • If else to a 1 line statement
• Only a simple if else and needs to be same variable

Variable = (condition) ? expr1 : expr2


If (bit1 & 2
{
        bit1 =1;
}
Else
{
        Bit1 = 0;
}
Ternary if


Bit1 = (bit1 % 2) ? 1 : 0;

two-dimensional array

• Split up in row columns [0][0]
• [] rows [] columns
• [6] [4] 6 1diminesional arrays with 4 cells

When passing 1d array dont specify value First dimension blank when passing 2d array but not the 2nd [][5] Calling them just the name

Passing parameters to functions

Two basic methods

• Pass by value
  • A copy is made when you pass
• Pass by references
  • Pass it by the addresses storage location
  • Operations are done directly on parameter

In C

• All parameters pased by value
• No ability to pass by reference does not exist
• Arrays are exceptions by using pointers which simulate it

segmentation faults

• When u do something bad
• When you attempted to access a restricted area of memory,
• The operating system is not happy about this

Debugging

• Is a tool to help you locate logic problems
• Also shows the line of code causing segfault
• Printing to screen is not as effective due to buffering
  • Its waste of time with print statements
  • Debug is faster
  • Printing is buffered, when program died, buffer dies
• This is a weapon against logic issues Why use GDB and not some other debug
• Works on any unix linux system
• Widley available
• Works with RPI
  • Many ides use the same words, but use icons stead of typing
  • Learning them on cml helps you learn debugging in general
• GDB: The GNU Project Debugger
  • When you compile your program you need to run the option to add debugging
    • -g
    • Gdb a.out
    • Quit
    • Most debug commands can be run by their first letter
  • List
    • List 1- will show the first 10 lines of the program
    • List n- will show the 5 lines before n and 4 lines after n 10 lines
    • List x,y - will show lines x through y
    • List function_name - wil show 4 lines before and after start of function
  • Break on main -always
  • Run - start program
  • Print /t prints int in binary
  • Print /x - print int in hex
  • Ptype - way to see definition of variable
• Step
  • Steps into function
• Next
  • Executes line of code
  • Doesnt go into function but executes it all
• Watch
  • Sets watchpoint for an expression
    • Gdb will break when the expression is written into by the pgram and its values change
• Backtrace - display which functions have been called