Foundations

Loops

Go uses for for counted loops, range loops, and while-style loops.

for loop Go uses `for` as its only loop keyword.

Loops

limit
loop_intro.go
Replay: real traced execution (multi-file project)
package main

import "fmt"

func main() {
	var limit = 4
	total := 0

	for number := 1; number <= limit; number++ {
		total += number
	}

	fmt.Println("limit=", limit)
	fmt.Println("total=", total)
}

package main

import "fmt"

func main() {
	var limit = 2
	total := 0

	for number := 1; number <= limit; number++ {
		total += number
	}

	fmt.Println("limit=", limit)
	fmt.Println("total=", total)
}

package main

import "fmt"

func main() {
	var limit = 6
	total := 0

	for number := 1; number <= limit; number++ {
		total += number
	}

	fmt.Println("limit=", limit)
	fmt.Println("total=", total)
}

  1. limit ← 4, total ← 0

    5func main() {6  var limit→ 4 = 4 //@limit=2, 67  total→ 0 := 0

  2. total ← 1

    pass 1 of 4
    9for number1 := 1; number <= limit4; number++ {10  total→ 1 += number111}
    All 4 passes — pass 1 is the card above
    passnumbertotal
    110 → 1
    221 → 3
    333 → 6
    446 → 10

  3. fmt.Println("limit=", limit)

    13  fmt.Println("limit=", limit4)14  fmt.Println("total=", total10)15}
    outputlimit= 4
total= 10

  1. limit ← 2, total ← 0

    5func main() {6  var limit→ 2 = 27  total→ 0 := 0

  2. total ← 1

    pass 1 of 2
    9for number1 := 1; number <= limit2; number++ {10  total→ 1 += number111}

  3. total ← 3

    pass 2 of 2
    9for number2 := 1; number <= limit2; number++ {10  total→ 3 += number211}

  4. fmt.Println("limit=", limit)

    13  fmt.Println("limit=", limit2)14  fmt.Println("total=", total3)15}
    outputlimit= 2
total= 3

  1. limit ← 6, total ← 0

    5func main() {6  var limit→ 6 = 67  total→ 0 := 0

  2. total ← 1

    pass 1 of 6
    9for number1 := 1; number <= limit6; number++ {10  total→ 1 += number111}
    All 6 passes — pass 1 is the card above
    passnumbertotal
    110 → 1
    221 → 3
    333 → 6
    446 → 10
    5510 → 15
    6615 → 21

  3. fmt.Println("limit=", limit)

    13  fmt.Println("limit=", limit6)14  fmt.Println("total=", total21)15}
    outputlimit= 6
total= 21

Follow the Loop

  1. limit starts at 4.
  2. total starts at 0.
  3. The loop adds 1, then 2, then 3, then 4.
  4. total becomes 10.
  5. The program prints limit= 4 and total= 10. | limit | numbers added | total | | --- | --- | --- | | 2 | 1, 2 | 3 | | 4 | 1, 2, 3, 4 | 10 | | 6 | 1, 2, 3, 4, 5, 6 | 21 |

Exercise: loop_intro.go

Reproduce total= 10 for limit 4, then try limit 2 and 6 and predict each total before running it.