Week 6Jordan Jozwiak

After CS50…Before CS50…

Quiz 0O Thoughts?

O StatisticsO Mean: 73O Median: 75O Std Dev: 15

This WeekO HexadecimalO Enumerated TypesO StructsO File I/O

Hexadecimal NumbersO Hexadecimal is a way of

representing numbers in base 16, with each digit ranging from 0 – F.

O We usually represent numbers in base 10 and in binary we represent numbers in base 2, this is just one more way!0 1 2 3 4 5 6 7 8 9 1

011

12

13

14

15

0 1 2 3 4 5 6 7 8 9 A B C D E F

Hexadecimal NumbersO Hexadecimal is useful because it

gives us a concise way of representing values in memory.

O Every set of 4 bits (a ‘nibble’, or half a ‘byte’) can be represented by 1 hex digit!

1 0 0 1 1 1 1 0 0 1 1 1 0 0 0 1

9 E 7 1

Hexadecimal NumbersO Notationally, we write hexadecimal

numbers preceded by ‘0x’, which simply denotes that what follows is a hexadecimal number.

O The below value might be written: 0x9E71

1 0 0 1 1 1 1 0 0 1 1 1 0 0 0 1

9 E 7 1

Enumerated Types

O Allows us to create our own type with a finite set of possible values.

O Abstraction makes code easier to understand and work with.

Enumerated TypesExamples of Possible Finite Sets:O {WIN, LOSE, DRAW}O {YES, NO, MAYBE}O {SMALL, MEDIUM, LARGE, XL}O {TALL, VENTI, GRANDE}O {WINDOWS, MAC_OS, LINUX}

intmain(){

enum { SUCCESS, FAILURE };return SUCCESS;

}

enum day{

SUNDAY,MONDAY,TUESDAY,WEDNESDAY,THURSDAY,FRIDAY,SATURDAY

};enum day get_next_day(enum day d);enum day get_today();

int main(){

enum day today, tomorrow;today = get_today();tomorrow = get_next_day(today);...

}

Enum with typedefsenum suit {HEARTS, CLUBS, DIAMONDS, SPADES};enum suit mySuit1 = CLUBS;enum suit mySuit2 = DIAMONDS;enum suit mySuit3 = HEARTS;

but it’s slightly more economical to write…typedef enum {HEARTS, CLUBS, DIAMONDS, SPADES} suit;suit mySuit1 = CLUBS;suit mySuit2 = DIAMONDS;suit mySuit3 = SPADES;

Consider how well this would work with a switch statement!

Structs

O Structs provide a way of bundling together related values.

O Sets of ‘fields’ – variables each having their own distinct data types.

O Useful when we want to keep track of multiple related properties.

Struct

O Can access fields within a struct:O NameOfStruct.NameOfField

O Can access fields from a pointer to a struct:O Pointer->NameOfFieldO (*struct).NameOfField

Structs

struct pkmn{ char* name; char* type; int hp;};

Structs “.” vs “->”typedef struct date{

int year;int month;int day;struct date *tomorrowp;

}date;

If datep were a pointer to the struct:date * datep = malloc(sizeof(date));

datep->tomorrowp->daydate.tomorrowp->day

Structs

struct pkmn charmander;charmander.name = GetString();charmander.type = GetString();charmander.hp = 40;

Structtypedefstruct {

char *name;char* type;int hp;

} pkmn;

// no longer need to

// write ‘struct pkmn’!

pkmn mudkip;

File I/O

O We are accustomed to reading from and writing to the terminal.

O More formally, we read from stdin, write to stdout.O We can also read from and write to files!

File I/OO fopen – open a fileO fclose – close a fileO fread – read from a fileO fwrite – write from a fileO fseek - move to a particular point in a file

File I/OO Must always open a file before

reading from or writing to it.O Should always close a file whenever

you open one!

File I/OO fopen returns a FILE*, a pointer to a

‘file handle’. O We use the FILE* to access and close

our file.

Coding time!! :DO In the CS50 Appliance…

O cloud.cs50.net/~jjozwiak