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This is CS50

Visit cs50.ly/screen to view projector on your laptop and ask questions via chat.
Today's snacks will be whoopie pies! 🟤
If coughing or not feeling well, do just leave early and watch online!
If you'd like to attend this week's (free) CS50 Lunch at Changsho (up Mass Ave) �on Fri 9/30 at 1:15pm, RSVP at cs50.ly/lunch!
Do say hi or ask questions during break or after class!

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Happy Birthday to Xochi! 🥳

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cs50.ly/art

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RGB

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

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

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

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0 1 2 3 4 5 6 7 8 9 a b c d e f

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hexadecimal

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base-16

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# #

16¹

16⁰

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# #

16

1

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+

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1

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+

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FF

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1

240

15

+

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FF

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255

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F

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1111

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11111111

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FF

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0	1	2	3	4	5	6	7
8	9	10	11	12	13	14	15
16	17	18	19	20	21	22	23
24	25	26	27	28	29	30	31

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0	1	2	3	4	5	6	7
8	9	A	B	C	D	E	F
10	11	12	13	14	15	16	17
18	19	1A	1B	1C	1D	1E	1F

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0	1	2	3	4	5	6	7
8	9	A	B	C	D	E	F
10	11	12	13	14	15	16	17
18	19	1A	1B	1C	1D	1E	1F

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0x0	0x1	0x2	0x3	0x4	0x5	0x6	0x7
0x8	0x9	0xA	0xB	0xC	0xD	0xE	0xF
0x10	0x11	0x12	0x13	0x14	0x15	0x16	0x17
0x18	0x19	0x1A	0x1B	0x1C	0x1D	0x1E	0x1F

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int n = 50;

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				50 n

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				50 0x123

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&

*

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pointers

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int n = 50;

int *p = &n;

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				50 n

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				50 0x123

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0x123 p

				50 0x123

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0x123 p

				50 0x123

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p

				50 0x123

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string

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string s = "HI!";

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H	I	!	\0

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H s[0]	I s[1]	! s[2]	\0 s[3]

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H 0x123	I 0x124	! 0x125	\0 0x126

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0x123 s

	H 0x123	I 0x124	! 0x125	\0 0x126

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s

	H 0x123	I 0x124	! 0x125	\0 0x126	0x127

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string s = "HI!";

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string s = "HI!";

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char *s = "HI!";

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typedef struct

{

string name;

string number;

}

person;

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typedef struct

{

string name;

string number;

}

person;

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typedef struct

{

string name;

string number;

}

person;

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typedef struct

{

string name;

string number;

}

person;

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typedef int integer;

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typedef int integer;

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typedef int integer;

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typedef char *string;

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typedef char *string;

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typedef char *string;

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cs50.h

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pointer arithmetic

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pointer arithmetic

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string

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char *

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break

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s

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s





	H	I	!	\0

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s





	H 0x123	I 0x124	! 0x125	\0 0x126

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0x123 s





	H 0x123	I 0x124	! 0x125	\0 0x126

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0x123 s					t





	H 0x123	I 0x124	! 0x125	\0 0x126

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0x123 s					t





	H 0x123	I 0x124	! 0x125	\0 0x126		H	I	!	\0

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0x123 s					t





	H 0x123	I 0x124	! 0x125	\0 0x126		H 0x456	I 0x457	! 0x458	\0 0x459

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0x123 s					0x456 t





	H 0x123	I 0x124	! 0x125	\0 0x126		H 0x456	I 0x457	! 0x458	\0 0x459

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s					t





	H 0x123	I 0x124	! 0x125	\0 0x126		H 0x456	I 0x457	! 0x458	\0 0x459

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s

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s





	h	i	!	\0

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s





	h 0x123	i 0x124	! 0x125	\0 0x126

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0x123 s





	h 0x123	i 0x124	! 0x125	\0 0x126

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0x123 s					t





	h 0x123	i 0x124	! 0x125	\0 0x126

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0x123 s					0x123 t





	h 0x123	i 0x124	! 0x125	\0 0x126

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s					t





	h 0x123	i 0x124	! 0x125	\0 0x126

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s					t





	H 0x123	i 0x124	! 0x125	\0 0x126

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malloc

free

…

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s





	h 0x123	i 0x124	! 0x125	\0 0x126

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s					t





	h 0x123	i 0x124	! 0x125	\0 0x126

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s					t





	h 0x123	i 0x124	! 0x125	\0 0x126		0x456	0x457	0x458	0x459

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s					t





	h 0x123	i 0x124	! 0x125	\0 0x126		0x456	0x457	0x458	0x459

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s					t





	h 0x123	i 0x124	! 0x125	\0 0x126		h 0x456	0x457	0x458	0x459

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s					t





	h 0x123	i 0x124	! 0x125	\0 0x126		h 0x456	i 0x457	0x458	0x459

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s					t





	h 0x123	i 0x124	! 0x125	\0 0x126		h 0x456	i 0x457	! 0x458	0x459

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s					t





	h 0x123	i 0x124	! 0x125	\0 0x126		h 0x456	i 0x457	! 0x458	\0 0x459

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s					t





	h 0x123	i 0x124	! 0x125	\0 0x126		H 0x456	i 0x457	! 0x458	\0 0x459

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NULL

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valgrind

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garbage values

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int main(void)

{

int *x;

int *y;

x = malloc(sizeof(int));

*x = 42;

*y = 13;

y = x;

*y = 13;

}

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int main(void)

{

int *x;

int *y;

x = malloc(sizeof(int));

*x = 42;

*y = 13;

y = x;

*y = 13;

}

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int main(void)

{

int *x;

int *y;

x = malloc(sizeof(int));

*x = 42;

*y = 13;

y = x;

*y = 13;

}

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int main(void)

{

int *x;

int *y;

x = malloc(sizeof(int));

*x = 42;

*y = 13;

y = x;

*y = 13;

}

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int main(void)

{

int *x;

int *y;

x = malloc(sizeof(int));

*x = 42;

*y = 13;

y = x;

*y = 13;

}

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int main(void)

{

int *x;

int *y;

x = malloc(sizeof(int));

*x = 42;

*y = 13;

y = x;

*y = 13;

}

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int main(void)

{

int *x;

int *y;

x = malloc(sizeof(int));

*x = 42;

*y = 13;

y = x;

*y = 13;

}

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int main(void)

{

int *x;

int *y;

x = malloc(sizeof(int));

*x = 42;

*y = 13;

y = x;

*y = 13;

}

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void swap(int a, int b)

{

}

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void swap(int a, int b)

{

int tmp = a;

a = b;

b = tmp;

}

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void swap(int a, int b)

{

int tmp = a;

a = b;

b = tmp;

}

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scope

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↑

stack

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machine code

↑

stack

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machine code

globals

heap

↓

↑

stack

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machine code

globals

heap

↓

↑

stack

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machine code

globals

heap

↓

↑

stack

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machine code

globals

heap

↓

↑

stack

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machine code

globals

heap

↓

↑

stack

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↑

stack

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void swap(int a, int b)

{

int tmp = a;

a = b;

b = tmp;

}

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main

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main

swap

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main

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x

y

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1

x

2

y

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1

x

2

y

swap

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a

b

tmp

1

x

2

y

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1

a

2

b

tmp

1

x

2

y

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int tmp = a;

a = b;

b = tmp;

1

a

2

b

tmp

1

x

2

y

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int tmp = a;

a = b;

b = tmp;

1

a

2

b

1

tmp

1

x

2

y

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int tmp = a;

a = b;

b = tmp;

2

a

2

b

1

tmp

1

x

2

y

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int tmp = a;

a = b;

b = tmp;

2

a

1

b

1

tmp

1

x

2

y

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2

a

1

b

1

tmp

1

x

2

y

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1

x

2

y

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void swap(int a, int b)

{

int tmp = a;

a = b;

b = tmp;

}

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void swap(int *a, int *b)

{

int tmp = *a;

*a = *b;

*b = tmp;

}

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1

x

2

y

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a

b

tmp

1

x

2

y

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int tmp = *a;

*a = *b;

*b = tmp;

a

b

tmp

1

x

2

y

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int tmp = *a;

*a = *b;

*b = tmp;

a

b

1

tmp

1

x

2

y

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int tmp = *a;

*a = *b;

*b = tmp;

a

b

1

tmp

2

x

2

y

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int tmp = *a;

*a = *b;

*b = tmp;

a

b

1

tmp

2

x

1

y

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a

b

1

tmp

2

x

1

y

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2

x

1

y

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void swap(int a, int b)

{

int tmp = a;

a = b;

b = tmp;

}

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void swap(int *a, int *b)

{

int tmp = *a;

*a = *b;

*b = tmp;

}

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machine code

globals

heap

↓

↑

stack

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heap

↓

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stack

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heap overflow

stack overflow

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buffer overflow

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get_char

get_double

get_float

get_int

get_long

get_string

...

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scanf

...

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file I/O

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BMP