Foundations

Variables

Go variables hold typed values that can feed later expressions.

variable `var` declares a variable. Go infers the type from the value when no explicit type is written.

Variables

unitPrice
variables.go
Replay: real traced execution (multi-file project)
package main

import "fmt"

func main() {
	var unitPrice = 12
	quantity := 3
	total := unitPrice * quantity

	fmt.Println("unit=", unitPrice)
	fmt.Println("total=", total)
}

package main

import "fmt"

func main() {
	var unitPrice = 8
	quantity := 3
	total := unitPrice * quantity

	fmt.Println("unit=", unitPrice)
	fmt.Println("total=", total)
}

package main

import "fmt"

func main() {
	var unitPrice = 20
	quantity := 3
	total := unitPrice * quantity

	fmt.Println("unit=", unitPrice)
	fmt.Println("total=", total)
}

  1. unitPrice ← 12, quantity ← 3, total ← 36

    5func main() {6  var unitPrice→ 12 = 12 //@unitPrice=8, 207  quantity→ 3 := 38  total→ 36 := unitPrice12 * quantity3910  fmt.Println("unit=", unitPrice12)11  fmt.Println("total=", total36)12}
    outputunit= 12
total= 36

  1. unitPrice ← 8, quantity ← 3, total ← 24

    5func main() {6  var unitPrice→ 8 = 87  quantity→ 3 := 38  total→ 24 := unitPrice8 * quantity3910  fmt.Println("unit=", unitPrice8)11  fmt.Println("total=", total24)12}
    outputunit= 8
total= 24

  1. unitPrice ← 20, quantity ← 3, total ← 60

    5func main() {6  var unitPrice→ 20 = 207  quantity→ 3 := 38  total→ 60 := unitPrice20 * quantity3910  fmt.Println("unit=", unitPrice20)11  fmt.Println("total=", total60)12}
    outputunit= 20
total= 60

Follow the Total

  1. unitPrice starts at 12.
  2. quantity starts at 3.
  3. total := unitPrice * quantity multiplies 12 * 3.
  4. total becomes 36.
  5. The program prints unit= 12 and total= 36. | unitPrice | quantity | total | | --- | --- | --- | | 8 | 3 | 24 | | 12 | 3 | 36 | | 20 | 3 | 60 |

Exercise: variables.go

Reproduce unit= 12 and total= 36, then try unitPrice 8 and 20 and predict each total before running it.