Learn Go: Conditionals

A Go if statement evaluates a condition and executes a statement block enclosed in curly braces {..} if the evaluation returns true. The condition may be optionally enclosed inside a pair of parentheses (...).

if (healthy) {
  fmt.Println("Work.")
}
if sick {
  fmt.Println("Stay home.")
}

A Go else statement can succeed an if or if else-if statement block and its code executed if the conditions in the preceding if or if else-if statements evaluate to false.

sick := false
if sick {
  fmt.Println("Call the doctor.")
} else {
  fmt.Println("Enjoy your day.")
}

Go supports the standard comparison operators that compare two values and return a boolean. These include:

• == equivalence operator
• != not equal
• < less than
• > greater than
• <= less than or equal
• >= greater than or equal

  same := 3 == 3 
  // evaluates to true
  notsame := "ABC" != "abc" 
  // evaluates to true
  lessthan := 5 <= -5 
  // evaluates to false

In addition to comparison operators, Go also supports logical operators which evaluate boolean values and return a boolean value. For example:

• && is the AND operator that returns true if all the booleans are true
• || is the OR operator that returns true if one of the booleans is true
• ! is the NOT operator that returns the opposite of a boolean value

  answer := true && false 
  // returns false
  answer = true || false  
  // returns true
  answer = !false         
  // returns true

The Go else if statement provides an additional condition to evaluate besides the first if conditional. It can only appear after the if statement and before an else statement if it exists. For example:

if (temperature < 60) {
  fmt.Println("Put on a jacket.")
} else if (temperature >= 60 && temperature < 75) {
  fmt.Println("Put on a light sweater.")
} else {
  fmt.Println("Wear summer clothes.")
}

Multiple else if statements can exist alongside the if statement. The if else if statements are scanned from top to bottom and only the code block associated with a true condition is executed. If none of the conditions are satisfied, the else code block is executed if it exists.

A short variable declaration can be made within the scope of an if or switch statement before the condition is specified but after the if or switch keyword. A semicolon, ;, is appended to the declaration to separate it from the condition.

if age := 55; age >= 55 {
  fmt.Println("You are retiring!")
}
switch season := "spring"; season {
  case "spring":
    fmt.Println("Plant some bulbs.")
  case "summer":
    ...
}

The Go switch statement can be used as an alternative to a set of if followed by else if statements. The switch statement compares the expression inside a condition with a set of values encapsulated in cases. The code inside a matched case value is executed and the switch block terminates. A default case without a value can be appended to the last case and its code executed if no prior match is found.

day := "Tuesday"
switch day {
  case "Monday":
    fmt.Println("Monday is magnificent.")
  case "Tuesday":
    fmt.Println("Tuesday is terrific.")
  case "Wednesday":
    fmt.Println("Wednesday is wacky.")
  default:
    fmt.Println("We survived.")
}

A seed value in Go is used for generating random numbers. By default, the seed value is 1 and this leads to a predictable number instead of random. To make the seed value unique, call the seed function, rand.Seed(), with the argument time.Now().UnixNano() to return the difference in time (in Nanoseconds) since Janurary 1st 1970.

rand.Seed(time.Now().UnixNano())

Go provides a function, math.rand.Intn(), in the math.rand package to generate a random number. To generate such a number between 0 to 99, pass 100 as the function argument.

number := math.rand.Intn(100)