Foundations

Loops

Loops repeat a block while a counter changes.

for loop A `for` loop can initialize a counter, test a condition, and update the counter after each pass.

Loops

limit
Loops.cs
Replay: real traced execution (multi-file project)
using System;

class Program
{
    static void Main()
    {
        int limit = 4;
        int total = 0;

        for (int number = 1; number <= limit; number++)
        {
            total += number;
        }

        Console.WriteLine($"limit={limit}");
        Console.WriteLine($"total={total}");
    }
}

using System;

class Program
{
    static void Main()
    {
        int limit = 2;
        int total = 0;

        for (int number = 1; number <= limit; number++)
        {
            total += number;
        }

        Console.WriteLine($"limit={limit}");
        Console.WriteLine($"total={total}");
    }
}

using System;

class Program
{
    static void Main()
    {
        int limit = 6;
        int total = 0;

        for (int number = 1; number <= limit; number++)
        {
            total += number;
        }

        Console.WriteLine($"limit={limit}");
        Console.WriteLine($"total={total}");
    }
}

  1. limit ← 4, total ← 0

    4{5    static void Main()6    {7        int limit→ 4 = 4; //@limit=2, 68        int total→ 0 = 0;

  2. total ← 1

    pass 1 of 4
    10for (int number1 = 1; number <= limit4; number++)11{12    total→ 1 += number1;13}
    All 4 passes — pass 1 is the card above
    passnumbertotal
    111
    223
    336
    4410

  3. Console.WriteLine($"limit={limit}");

    15    Console.WriteLine($"limit={limit4}");16    Console.WriteLine($"total={total10}");17}
    outputlimit=4
total=10

  1. limit ← 2, total ← 0

    4{5    static void Main()6    {7        int limit→ 2 = 2;8        int total→ 0 = 0;

  2. total ← 1

    pass 1 of 2
    10for (int number1 = 1; number <= limit2; number++)11{12    total→ 1 += number1;13}

  3. total ← 3

    pass 2 of 2
    10for (int number2 = 1; number <= limit2; number++)11{12    total→ 3 += number2;13}

  4. Console.WriteLine($"limit={limit}");

    15    Console.WriteLine($"limit={limit2}");16    Console.WriteLine($"total={total3}");17}
    outputlimit=2
total=3

  1. limit ← 6, total ← 0

    4{5    static void Main()6    {7        int limit→ 6 = 6;8        int total→ 0 = 0;

  2. total ← 1

    pass 1 of 6
    10for (int number1 = 1; number <= limit6; number++)11{12    total→ 1 += number1;13}
    All 6 passes — pass 1 is the card above
    passnumbertotal
    111
    223
    336
    4410
    5515
    6621

  3. Console.WriteLine($"limit={limit}");

    15    Console.WriteLine($"limit={limit6}");16    Console.WriteLine($"total={total21}");17}
    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: Loops.cs

Reproduce total=10 for limit 4, then use the pinned limits 2 and 6 to predict each total.