1.4.1 Data types

Question 1

What is static typing?

Answer 1

When variables have to be defined as a certain data type before they can be used.

Question 2

What is dynamic typing?

Answer 2

When variables do not have to be defined before they are used and can be defined when needed.

Question 3

Name 4 different data types.

Answer 3

String, Boolean, Integer, Float/Real

Question 4

What is strong typing?

Answer 4

When variables are locked into a set data type and will not work if used as different data types.

Question 5

What is weak typing?

Answer 5

When variables are not locked to a certain data type and can be used as multiple data types.

Question 6

What is a primitive data type?

Answer 6

A data type that is provided by a programming language.

Question 7

Name 5 primitive data types.

Answer 7

Integer
String
Real / Float
Boolean
(Character)

Question 8

How do we convert between denary and hexadecimal?

Answer 8

Denary to Hex:
Divide by 16 = First Number
Remainder = Second Number

Question 9

How do we convert a number from hex to denary/

Answer 9

Multiply first number by 16.

Add on second number.

Question 10

What are the numbers 10-15 represented by in hexadecimal?

Answer 10

A B C D E F

Question 11

How do we convert a number from binary to hex?

Answer 11

Split in to nibbles
First nibble = first number
2nd nibble = second number
so on…

Question 12

How do we convert from Hex to binary?

Answer 12

First number = first nibble
2nd number = second number
so on…
combine nibbles

Question 13

Why is hexadecimal used?

Answer 13

Because they are easier to remember and write / type for humans

Question 14

What are the rules for binary addition?

Answer 14

0 + 0 = 0
1 + 0 = 1
1 + 1 = 0 (carry 1)
1 + 1 + 1 = 1 (carry 1)

Question 15

What is an overflow error?

Answer 15

When two binary numbers are added together and the new value exceeds the maximum number of bits allowed.

Question 16

How do we represent negative numbers using sign and magnitude?

Answer 16

We make the leftmost bit (the most significant bit) a sign bit.

If this is 0, the number is positive

If this is 1 the number is negative

Question 17

Using sign and magnitude, is this number positive or negative?

10010101

Answer 17

Negative

Question 18

Why is sign and magnitude not used?

Answer 18

Because it does not work with binary arithmetic.

Question 19

How do we represent negative numbers using two’s complement?

Answer 19

The most significant bit is a negative value.
e.g.
With 8 bits, the MSB will equal -128.

Question 20

What is the greatest number that can be represented with 8 two’s complement bits.

Answer 20

127

Question 21

How can we represent a negative denary number in binary using twos complement?

Answer 21

Work out positive equivalent of number in binary.
Flip all of the bits
Add 1.

Question 22

How can we convert from a negative binary number in twos complement to a denary number?

Answer 22

Flip all of the bits and add 1.

Convert to denary to find positive equivalent.

Question 23

How do we carry out binary subtraction using twos complement?

Answer 23

Number to subtract = negative and then add the numbers together using normal binary addition rules.

Question 24

What is fixed point binary?

Answer 24

When we determine how many numbers there will be before and after a decimal point, in order to hold floats.

e. g. 4 before and after
3. 75 = 0011 1100 (3) (0.75)

Question 25

What is floating point binary?

Answer 25

When we store a float in a format where the decimal point is not in a fixed location.

Question 26

Where must the decimal point be in a normalised floating point number?

Answer 26

Between the first and second leftmost bits.

Question 27

What will the first two leftmost bits of a positive, normalised, floating point binary number always be?

Answer 27

01

All the repeating 0s before mean the same as a singe 0

Question 28

What will the first two leftmost bits of a negative, normalised, floating point binary number always be?

Answer 28

10

All repeating 1s before mean the same as the single 1 here. -128 + 64 + 32 == -32

Question 29

How do we add/subtract decimal binary numbers?

Answer 29

Denormalise the numbers
Align the decimal points
Carry out binary addition / subtraction as normal
Normalise the result

Question 30

What is an underflow error?

Answer 30

When a number is too small to be represented in the allotted number of bits.

e.g. 0.00005 / 200

Question 31

What is a logical shift?

Answer 31

When all the bits move left or right.

RHS: Least significant bit moves into carry bit and zero replaces most significant bit

LHS: Most significant bit moves into carry bit and zero replaces least significant bit

Question 32

What are logical shifts used for?

Answer 32

Examining the least significant but of a number.

Question 33

What is an arithmetic shift?

Answer 33

The same as a logical shift, but the sign bit must always remain the same.

Question 34

What effect does a left arithmetic shift have on a number?

Answer 34

Multiplies by 2

Question 35

What effect does a right arithmetic shift have on a number?

Answer 35

Divides by 2

Question 36

How would you multiply by a non multiple of 2 in binary?

Answer 36

Use a combination of shifts and addition.

Question 37

What is a circular shift?

Answer 37

When the value moved out to the carry bit in a shift is added onto the other end of the number.

Question 38

Why do we use circular shifts?

Answer 38

If we are performing shifts in multiple bytes.

E.g. two registers used to store a 16 bit integer.

Question 39

What is masking useful for?

Answer 39

Allowing the CPU to manipulate individual bits in the operand, check for values and either allow or block bits.

Question 40

What is the AND mask useful for?

Answer 40

Checking conditions stored in a binary value.

Question 41

What is the OR mask useful for?

Answer 41

Resetting individual bits in a binary value.

Question 42

What is the XOR mask useful for?

Answer 42

Checking that two bits are not the same.