Control Flow

If and Else

An if statement chooses one block when a condition is true and another when it is false.

branch A branch is the block of code selected by a condition.

If and Else

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

class Program
{
    static void Main()
    {
        int temperature = 68;
        string message;

        if (temperature >= 70)
        {
            message = "warm";
        }
        else
        {
            message = "cool";
        }

        Console.WriteLine($"temperature={temperature}");
        Console.WriteLine($"message={message}");
    }
}

using System;

class Program
{
    static void Main()
    {
        int temperature = 50;
        string message;

        if (temperature >= 70)
        {
            message = "warm";
        }
        else
        {
            message = "cool";
        }

        Console.WriteLine($"temperature={temperature}");
        Console.WriteLine($"message={message}");
    }
}

using System;

class Program
{
    static void Main()
    {
        int temperature = 85;
        string message;

        if (temperature >= 70)
        {
            message = "warm";
        }
        else
        {
            message = "cool";
        }

        Console.WriteLine($"temperature={temperature}");
        Console.WriteLine($"message={message}");
    }
}

  1. temperature ← 68

    4{5    static void Main()6    {7        int temperature→ 68 = 68; //@temperature=50, 858        string message;

  2. message ← cool

    13}14else15{16    message→ cool = "cool";17}

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

    19    Console.WriteLine($"temperature={temperature68}");20    Console.WriteLine($"message={messagecool}");21}
    outputtemperature=68
message=cool

  1. temperature ← 50

    4{5    static void Main()6    {7        int temperature→ 50 = 50;8        string message;

  2. message ← cool

    13}14else15{16    message→ cool = "cool";17}

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

    19    Console.WriteLine($"temperature={temperature50}");20    Console.WriteLine($"message={messagecool}");21}
    outputtemperature=50
message=cool

  1. temperature ← 85

    4{5    static void Main()6    {7        int temperature→ 85 = 85;8        string message;

  2. message ← warm

    10if (temperature85 >= 70)11{12    message→ warm = "warm";13}

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

    19    Console.WriteLine($"temperature={temperature85}");20    Console.WriteLine($"message={messagewarm}");21}
    outputtemperature=85
message=warm

Choose Warm or Cool

  1. temperature starts at 68.
  2. The condition temperature >= 70 is false.
  3. The else branch runs.
  4. message becomes cool. | Temperature | Branch | Message | | --- | --- | --- | | 50 | else | cool | | 68 | else | cool | | 85 | if | warm |

Exercise: IfElse.cs

Use if and else to print warm for temperatures at least 70 and cool otherwise