Lecture 2

Question 1

What are the data types which represent numerical values?

Answer 1

• short 1-byte
• int 4-bytes
• long 4-bytes

Question 2

char

Answer 2

• It represents one of 256 different characters.
• we pay intention to 75 of them.
• Why 256? because of 2 ~8 - 1= 255
• When we say here 256 characters, but in the meanwhile, you could place only 255 digits in the binary representation for 1 byte/8bit. the answer is => Zero is considered a char here (by the way NULL), so 255 + 0 or null
• In this case, we used all the 8 bits. shouldn’t we use all the byte and this should be normal? no in other cases we used the most left bit as a sign bit [+ -
• https://ykode.id/under-the-bonnet-representing-characters-and-strings-ff7cec26ee3c

Question 3

What are the data types which represent fractional number values?

Answer 3

• float 4-bytes

- double 8-bytes

Question 4

What is the binary digit?

Answer 4

• high or low voltages
• computer scientists don’t need to view it that way, they
  just need to recognize that a bit is a very small amount of memory that can distinguish between 2 different values
• a single bit can store zero or one

Question 5

How do we represent a boolean in memory?

Answer 5

• 1 byte
• a boolean could just be mapped to a single bit in memory
• it turns out it’s not practical to do that but if you really wanted to use a single bit to represent a boolean variable you could engineer your compiler to do that

Question 6

How to convert binary to decimal?

Question 7

how to add binary numbers?

Answer 7

1 + 1 = 0 :]

Question 8

how to add binary numbers?

Answer 8

1 + 1 = 0

1 + 1 + 1 = 1

Question 9

How to represent a negative number in binary

Answer 9

• represent the number as you do in positive case
• flip all the numbers
• add one to this number
  0101
  ……..
  1010
  0001
  …….
  1011
• when the number gets bigger overflow will happen.

Question 10

What short represents?

Answer 10

negative 2 to the 15th through 2 to the 15th minus 1

Question 11

what happen when I assign short to int and the value is negative?

Answer 11

sign bit extend

Question 12

bit patten evaluation

Answer 12

int i =5;
float f = i;
cout<

Question 13

5.0 representation

Answer 13

1.25 x 2~2
exp = 129
xxx = .25

Question 14

When the float evaluation could be mistakenly ignored?

Answer 14

in a case like this:

int i = 37;
float f = * (float*)&i;

please read from the right to the left!

we cheated here by casting the ptr to float while the actual bit pattern represents an int,

The compiler will think that bit evaluation is not important so it will copy it, which will give another number