learngo/09-go-type-system/questions/01-questions-predeclared-types.md

Which one is not a predeclared data type of Go?

1. int
2. float64
3. uint64
4. uint
5. duration CORRECT
6. int8
7. rune
8. byte
9. float32
10. complex128

What's a predeclared data type?

1. A data type used only in the compiler
2. A built-in data type that comes with Go that you can use it from anywhere without importing any package CORRECT
3. The data type of a variable

By using only 8 bits, how many different numbers or states can you represent?

1. 8
2. 16
3. 256 CORRECT
4. 65536

3: 2^8 is 256, so you can represent 256 different states.

How many bits 2 bytes contains?

1. 2
2. 8
3. 16 CORRECT
4. 32
5. 64

What's the output of the following code?

fmt.Printf("%08b = %d", 2, 2)

1. 00000001 = 2
2. 00000010 = 2 CORRECT
3. 00000100 = 2
4. 00001000 = 2

EXPLANATION = From right to left, each bit goes from 2^0 to 2^(n - 1).

1: EXPLANATION. Here: 1 is the first digit from the right. So, it is 2^(1 - 1) = 2^0 = 1.

2: EXPLANATION. Here: 1 is the second digit from the right. So, it is 2^(2 - 1) = 2^1 = 2.

3: EXPLANATION. Here: 1 is the third digit from the right. So, it is 2^(3 - 1) = 2^2 = 4.

4: EXPLANATION. Here: 1 is the fourth digit from the right. So, it is 2^(4 - 1) = 2^3 = 8.

How many bytes of memory does an int64 value use?

1. 4
2. 8 CORRECT
3. 32
4. 64

2: 1 byte is 8 bits and int64 is 64 bits. So, 64/8=8 bytes.

How many bytes are needed to store a value of uint32 type?

1. 4 CORRECT
2. 8
3. 32
4. 64

2: 1 byte is 8 bits and uint32 is 32 bits. So, 32/8=4 bytes.

What's the size of int data type?

1. Depends: 32 bits or 64 bits. CORRECT
2. 32 bits
3. 64 bits

1: That's right. Go can change its size at the compile-time depending on which target machine you're compiling your program into.

English letters can be represented by the numbers within the range of: 0-255. For example, 'A' can be 65. Or, 'B' can be 66. So, what's the best data type for storing an English letter?

1. byte CORRECT
2. rune
3. int64
4. float64

1: That's right. A byte can represent 0-255 different values. So, it's a great fit for representing English letters, and numbers.

2: In practice, you can do it with a rune value. However, rune is 32-bits long and it can store almost every letter in existince. I'm asking for the optimal data type. Try again.

3: That would be too large for only 255 different numbers.

4: Float is not the best data type for numbers without fractional parts.

What does the following code print?

var letter uint8 = 255
fmt.Print(letter + 5)

1. 0
2. 4 CORRECT
3. 5
4. 260

2: Unsigned integers wrap around after their maximum capacity. Uint8's max is 255, so, if 255 + 1 is 0, then 255 + 5 is 4.

3: You're very close.

4: Uint8's max capacity is 255. It can't be 260.

What does the following code print?

var num int8 = -128
fmt.Print(num - 3)

1. -131
2. 125 CORRECT
3. -125

1: int8's min capacity is -128. It can't be -131.

2: Signed integers wrap around after their minimum capacity. int8's min is -128, so, if -128 - 1 is 127, then -128 - 3 is 125.