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This is CS50

If you'd like to attend CS50 Lunch this Fri 10/3 at 1:15pm, RSVP at cs50.ly/lunch!
On today's snack menu, clementines 🍊 and fruit snacks 🍬.
Do say hi or ask questions during break or after class!

What do today's binary bulbs spell?

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pixel art

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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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00

16

1

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01

16

1

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16

1

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16

1

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16

1

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16

1

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16

1

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16

1

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16

1

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16

1

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0A

16

1

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0B

16

1

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0C

16

1

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0D

16

1

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0E

16

1

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0F

16

1

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16

1

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1

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1

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16

1

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14

16

1

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…

16

1

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FF

16

1

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FF

16

1

16 × F

1 × F

+

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FF

16

1

16 × 15

1 × 15

+

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FF

16

1

240

15

+

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FF

16

1

255

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FF

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F F

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1111 1111

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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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%p

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pointers

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int n = 50;

int *p = &n;

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int n = 50;

int *p = &n;

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int n = 50;

int* p = &n;

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int n = 50;

int * p = &n;

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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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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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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

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typedef int

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typedef int integer;

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typedef

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typedef char *

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typedef char *string;

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typedef char *string;

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typedef uint8_t BYTE;

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typedef uint8_t BYTE;

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typedef uint8_t BYTE;

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cs50.h

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pointer arithmetic

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0x123 s

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

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50 i				50 j

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strcmp

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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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passing by value

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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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int x = 1;

int y = 2;

1

x

2

y

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swap(x, y);

1

x

2

y

swap

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swap(x, y);

a

b

tmp

1

x

2

y

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void swap(int a, int b);

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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passing by reference

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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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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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swap(x, y);

1

x

2

y

swap

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swap(x, y);

a

b

tmp

1

x

2

y

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void swap(int *a, int *b);

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

↓

↑

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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get_int

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scanf

…

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	50 n

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s

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s

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s

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s

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file I/O

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fopen

fclose

fprintf

fscanf

fread

fwrite

fseek

…

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BMP