01-22 (memory stuff)

square root thingy. My guess:

Main

1. (no params)
2. int a in main
3. int b in main
4. <return> for main = 0
5. (calling pythangoras)
   1. double a = 1.0 for a
   2. double b = 1.0 for b
   3. double c (empty)
   4. <return> = 0
   5. (Now c gets square root:)
      1. double x = (2.0)
      2. double guess = 0.0
      3. double up
      4. double down
      5. double mid
      6. <return> = 0

pacos: Main:

• a: int = junk
• b: int = junk
• <return>: int = junk Pythagoras:
• a: double = 1.0
• b: double = 1.0
• c: double = junk
• <return>: double = junk (then 0) Sqrt:
• x: double = 2.0
• guess: double = 0.0
• up: double = junk
• dn: double = junk
• mid: double = junk
• <return>: double = junk (then 0)

where do intermediate expressions live? In the CPU! i.e., when calling square_root((a*a + b*b)), the expression a*a + b*b is evaluated and stored in the cpu.

let guess be the sqrt. mid is prolly the average of up and dn. use a for loop

we keep looping while the imprecision is too big we start guess at 0. We keep increasing it by the midpoint between the up and dn If the guess*guess is too big, then up = guess*guess if guess times guess is too small, then down = guess times guess then we let guess = mid point and repeat.

char one_string[10];
printf("String: %s", one_string);

The above can print 1000 characters or 0 characters. it’s all luck when the print eventually hits a delimiter

void p1(void)
{
	char s1[10];
	printf("%s\n", s1);
}
void p2(void)
{
	char two_string[10];
	two_string[0] = 'T';
	two_string[1] = 'W';
	two_string[2] = 'O';
	two_string[3] = '!';
	two_string[4] = '\n';
	two_string[5] = 0;
	printf("%s\n", two_string);
}
 
void main(void)
{
	p2();
	p1();
	// This prints Two!\b twice
}

Basically it prints TWO! twice because the memory is freed from the previous call and is junk, but is then taken by s1 and it so happens to be the values set in p2.

• This is not always bound to happen. it’s merely a coincidence. On my computer, it usually happens though. Then if you reserve a string of size 100, there is a good chance that TWO! is in there. Remember that the places where memory is stored is often quite random. For instance, if you:

1. Store 100 ’+’ signs in a char array of size 100 in one function
2. Store TWO! in another function.
3. Print 100 random characters You might see the TWO! at the start, near the center, really anywhere the computer can find that’s convenient.