116 lines
2.3 KiB
Markdown
116 lines
2.3 KiB
Markdown
## What's a magic value?
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1. A value which pops up from somewhere
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2. Merlin the Wizard's spell
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3. An unnamed constant value in the source code *CORRECT*
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4. A named constant
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## What's a named constant?
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1. A constant with a cool name
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2. A constant value declared with a name *CORRECT*
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3. A literal value converted to a name
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## How to declare a constant?
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1. `Const version int = 3`
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2. `const version int := 3`
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2. `const version int = 3` *CORRECT*
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> **1:** "C"onst should be just "c"onst.
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>
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## Which code below is correct?
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1. `s := "pick me"; const length = len(s)`
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2. `const message = "pick me!"; const length = len(message)` *CORRECT*
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3. `const length = utf8.RuneCountInString("pick me")`
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> **1:** `s` not a constant.
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>
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> **2:** `len` function can be used as an initial value to a constant, when the argument to `len` is also a constant.
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>
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> **3:** You cannot call functions while initializing a constant.
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>
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## Which explanation below is correct for the following code?
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```go
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const speed = 100
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porsche := speed * 3
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```
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1. speed is typeless and porsche's type is int *CORRECT*
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2. speed's type is int and porsche's type is also int
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3. speed and porsche are typeless
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> **2:** speed has no type.
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>
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> **3:** A variable cannot be typeless.
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>
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## How to fix the following code?
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```go
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const spell string
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spell = "Abracadabra"
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```
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1. `const spell = "Abracadabra"` *CORRECT*
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2. `spell := "Abracadabra"`
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3. `var spell = "Abracadabra"`
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> **1:** A constant always have to be initialized to a value. And, sometimes the type declaration is not necessary.
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>
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> **2-3:** That's a variable not a constant.
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>
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## How to fix the following code?
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```go
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const total int8 = 10
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x := 5
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fmt.Print(total * x)
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```
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```go
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// #1 - *CORRECT*
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const total = 10
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x := 5
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fmt.Print(total * x)
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// #2
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const total int64 = 10
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x := 5
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fmt.Print(total * x)
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// #3
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const total int64 = 10
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x := 5
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fmt.Print(int64(total) * x)
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```
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> **1:** Now, the total constant is typeless, so it can be used with the x variable.
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>
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> **2:** There's still a type mismatch. x is int not int64.
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>
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> **3:** total is already int64. No need to convert it again.
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>
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## What are the values of the following constants?
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```go
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const (
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Yes = (iota * 5) + 2
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No
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Both
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)
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```
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1. Yes=0 No=1 Both=2
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2. Yes=2 No=3 Both=4
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3. Yes=7 No=12 Both=17
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4. Yes=2 No=7 Both=12 *CORRECT*
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> **3:** iota starts at 0, not 1.
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> |