6.00.1x & 6.00.2x

Question 1

imperative vs. declarative knowledge

Answer 1

declarative - statement of facts

imperative - recipe or “how-to” computation

Question 2

What is the difference between a program and a algorithm?

Answer 2

An algorithm is a conceptual idea, a program is a concrete instantiation (representation?) of an algorithm.

Question 3

A computational mode of thinking means that everything can be viewed as a math problem involving numbers and formulas.

True or False ?

Answer 3

True

Question 4

Computer Science is the study how to build efficient machines that run programs.

True or False ?

Answer 4

False

Question 5

What does it mean when we say that “the computer walks through the sequence executing some computation”?

Answer 5

The computer executes the instructions mostly in a linear sequence, except sometimes it jumps to a different place in the sequence.

Question 6

What are primitive operations and what are some examples of primitive operations ?

Where are they in a computional machine?

Answer 6

A low-level object or operation from which higher-level, more complex objects and operations can be constructed.

Examples: addition, subtraction, examine true or false statements

In the ALU - arithmetic logic unit

Question 7

What “Determines whether a string is legal”?

Answer 7

syntax

Question 8

What “determines whether a string as meaning”?

Answer 8

semantic syntax

Question 9

What “assigns a meaning to a legal sentence”?

Answer 9

semantics

Question 10

What is the output after each expression ?

Remember this is one session - each expression is calculated directly after the previous problem.

Answer 10

1. 5.0 and float
2. 4.0 and float
3. none type and error

Question 11

What sort of expression is this ?

and what value is returned ?

Answer 11

Bool

True

Question 12

print(ss[-4:-1])

How do you read slicing strings with negative index numbers ?

Answer 12

Same as positive

Read from left to right

remember starting value is inclusive

ending value is exclusive

Question 13

What is the significance of the stride in slicing ?

Answer 13

it allows you to choose the interval at which python takes parts when slicing

Question 14

How do you print in reverse order using slicing ?

Answer 14

Double colon to signify that this applies to the whole string

and then have -1 as the stride value.

Question 15

What is the return value of this piece of code ?

and why?

Answer 15

Hot

because the computer reads the code in a linar fashion and the value meets the if statement to ‘print’ HOT.

Question 16

What does += mean?

Answer 16

add whatever number to the varaible that is attached to it

mysum += i

Question 17

What is a recipe?

Answer 17

1. Sequence of simple steps
2. Flow of control process that specifies when each step is executed
3. A means of determining when to stop

Question 18

How many primitives do you need to do any calculation

Answer 18

6

Question 19

What are expressions ?

Answer 19

complex but legal combinations of primiives in a programming language

Question 20

What could go wrong when writing a program ?

Answer 20

Syntactic errors

Static syntactic errors

No semantic error but different meaning to what the programmer intended

Question 21

The difference between static semantics and semantics?

Answer 21

A statement in python may have meaning (it is statically semantically correct), but it may not do what you intended (it is not semantically correct).

Question 22

List all the operations on ints and floats

Answer 22

Question 23

How do you bind a value to a variable ?

Answer 23

Using the equals sign

e.g. pi = 3.14159

Question 24

What are the comparison operators for Ints and Floats ?

Answer 24

Question 25

Why is an indentation important?

Answer 25

Each indented set of expressions denotes a block of instructions.

Indentations also provide a visual structure that reflects the semantic structure of the program.

Question 26

What is a Branching program ?

Answer 26

The simplest branching statement is a conditional

A test ( an expression that evaluates to true or false )

A block of code to execute if the test is true

An optional block of code to execute if the test is false

Question 27

What is a nested conditional?

Answer 27

That inside a block, you have another conditional

Question 28

What does ‘control flow - branching’ do?

Answer 28

evaluates expressions in blocks if <condition> is <strong>True</strong></condition>

Question 29

For logical operator OR, what do you need to have a True output?

Answer 29

You need one True part of the statement

Question 30

True or False

Output ?

Answer 30

True

Question 31

BINDINGS: What would be the final answer ?

Answer 31

First as you go through the code you see that y is being assigned the value of ‘x’, which is 1.

So the new value of y is 1.

Now assigning the value of y to x, we know that y is 1 so the final value for x is 1

Question 32

STRINGS: How do you concatenate two strings with a space?

Answer 32

you have to add (with plus signs) to double quotation marks

Question 33

STRINGS: How do you find the length of string ?

What about spaces?

Answer 33

len( )

includes spaces

Question 34

STRINGS: If you index ‘eric’ with [1:3]

what is the output ?

Answer 34

The first element which is r

and the second element i

it doesn’t include the third element as you might think

In ranges like these when indexing you include the starting index element but the finishing index value is not included

Final output: ‘ri’

Question 35

STRINGS: what does the -1 mean for this string slicing?

Answer 35

a negative number means you count from the end of the array instead of the beginning.

Question 36

STRINGS: What result would this slicing have?

Answer 36

Every element except for the last one.

Question 37

STRINGS: What about this entail?

Answer 37

it would reverse the order of the string

Question 38

STRINGS: What would this return?

Answer 38

Nothing because it can’t step back any places when it is confined between 0 and 9.

You cannot start at 0 and count backwards to 9…

Question 39

STRINGS: How do you convert an integer into a string?

Answer 39

str(x)

where x is a variable holding the value

Question 40

INPUT/OUTPUT: Why were the quotation marks also printed?

How do end up with an int for the output value?

Answer 40

Because input simply expects everything to be a string.

Whatever I type it is going to read it in as a string.

Even if you inputted a number it is going to interpret it as a string of the characters of the number.

So you need to turn it into an int before you actually use it.

Question 41

INPUT/OUPUT: What is the ouput? And Why ?

Answer 41

The output is Hot

Code is ran linearly, from top to bottom, and it sees the “Hot” if statement first, and will never get to the “really Hot” elif statement because it already exited the loop at the first if.

Question 42

IDE: What is an IDE ?

Answer 42

Integrated development environment

Question 43

What do for and while loops do?

Answer 43

they can create an infinitely long looping of an expression(s) until it is stopped.

Question 44

Difference between for and while ?

Answer 44

for has a function integrated into it that allows you to define a range

Question 45

if you find this expression ..

mysum += i

i being a variable

what should think of ?

Answer 45

that some value is being added to mysum - mysum accumulates thes sums…

Question 46

Summarize for and while loops main features.

Answer 46

Question 47

When would you use a for loop?

And similarly, when would you use a for loop?

Answer 47

Use a for loop when you know what you are going to do as a computation

use a while loop when there is a condition that you can’t predict that would allow you to break out of the loop.

Question 48

EX vara varb: How could you have made the code shorter ?

Answer 48

instead of using ‘if’ clauses throughout you could have used ‘elif’ clauses after the first ‘if’ statement and that will have stopped you from having to test for ‘integers’ - the elif statement is only read if the first condition isn’t met. So if the condition is true it will have stopped there.

Question 49

Inside if statements that are inside ‘for’ and ‘while’ loops, if there is a break, what happens?

Answer 49

it stops the whole loop ( for or while )

Question 50

What do you need to remember about division in python?!

Answer 50

It always returns a float!

Question 51

What’s the answer to this question?

Why is it the way it is?

Answer 51

This is the answer as the code clearly states that after the count increase by 1 the loop should be broken…That means that no more iterations of the loop are going to take place, so the only printed value will be for the first letter ‘S’,

Question 52

Are space taken into account for a string in a for loop function!

Answer 52

yes !

spaces are also considered characters in python

Question 53

GUESS & CHECK: What is the output of an input function?

Answer 53

a string

Question 54

If you can remember, how did this work?

Answer 54

It worked because index was reset every time, due to the index = 0 variable. You can do this when the variable definition is inside the loop.

Question 55

What sort of input does the input function expect?

Answer 55

It expects a string.

So if you write something with double quotes attached, it will print the double quotes.

Question 56

How do you convert the input function from string to int?

Answer 56

write int() around the input function.

Question 57

What does the range option entail in a for loop?

Answer 57

Specifies what value you want the for loop to go to.

Question 58

how do you define a stop and step when using range

Answer 58

range(start, stop, step)

Question 59

what is important to remember about the stop value when using range?

Answer 59

the stop is actually equal to stop - 1

Question 60

What does this output ?

Answer 60

0.0, 1.0, 2.0, 3.0, 4.0

When you divide there the output is a float…

Question 61

What did you learn about the alphabet in python ?

Answer 61

that python recognizes alphabetical order, so you can simply test individual letters to see if one is higher up on the alphabet.

Question 62

What does an immutable type mean ?

Answer 62

You can’t change them.

They can’t be modified.

Question 63

How could you change a string?

Answer 63

You can’t change the string individually, you have to redefine the variable it is in.

Question 64

What does int(4.7) become in python?

Answer 64

4

Python simply truncates down.

Question 65

When slicing, is the final number inclusive or not?

Answer 65

Not inclusive, so if the range is 1:4, 4 is not included.

Question 66

How can you skip characters while slicing?

Answer 66

you add a third element to the slicing,

example

1:6:2

Question 67

What type does ‘input’ always use?

Answer 67

string

you need to enclose by int() if you want an integer.

Question 68

What is the order of growth of this function?

What did you learn?

Answer 68

The order of growth is O(log(b)).

Why? Well if you put in some testing values for b, like 16, you’ll notice that it takes 4 steps to get to b = 1, which can be represented by log₂ (16). The last step from 1 to 0 can be ignored because as b gets larger so does that step become more negligible. Similarly, if b is odd, there is one extra step that becomes negligible for large values of b.

The best way to approach these problems is to write down the general step equation for the whole function and then identify the dominant factor from there.

Question 69

Why is the big O of this function log(b)?

Answer 69

By converting the number into a string it is iterating over the characters of the string and not through the length of the number. For example, 110 is broken up as ‘1’, ‘1’ and ‘0’ as a string while as a number the for loop would go through every value until 110. By converting it into a string the function essentially divided by 10 on each iteration.

So the number of iterations through the loop can be seen as log(b).

You should remember this next time you see an integer being converted into a string, even though it probably isn’t the most effective method.

Question 70

If a recursive function calls the function twice in the return, what sort of complexity is it?

Answer 70

exponential