Goto and switch statements

Daily Knowledge Drop

The goto statement can be used to transfer control to a statement marked with a label, but it can also be used in a switch statement to transfer control to a different switch section using the switch case label.

This post, nor I, am endorsing the actual use of the goto statement - this post is for information purposes.

The goto statement is an unstructured code flow statement, making code difficult to read and maintain. For the most part, a structured control flow statement (if, continue, break, for) should be used.

goto

First we'll look at how the goto statement can be used normally, outside of a switch statement.

In this example:

• An int array is filled with random numbers between 0 and 100
• The array is search for any numbers between 50 and 60
• A relevant output message is displayed if a number was found or not

var randomNumbers = new int[20];

// populate the array with random numbers
Random randGen = new Random();
for (int i = 0; i < randomNumbers.Length; i++)
{
    randomNumbers[i] = randGen.Next(0, 100);
}

// iterate through each item and check the value
for (int i = 0; i < randomNumbers.Length; i++)
{
    if (randomNumbers[i] > 50 && randomNumbers[i] < 60)
    {
        // The goto statement is used to break out the loop 
        // if a relevant number is found and direct the 
        // flow to the `NumFound` label
        goto NumFound;
    }
}

Console.WriteLine("Number between 50 and 60 NOT FOUND");
// The goto statement is used to circumvent Console.WriteLine 
// method below, and direct the flow to the `Exit` label
goto Exit;

// Below, two labels are defined, each with a unique name

NumFound:
Console.WriteLine("Number between 50 and 60 FOUND");

Exit:
Console.WriteLine("Application closing");

For completeness, below is code sample (one of a possible many) on how the same can be achieved without using the goto statement:

var randomNumbers = new int[20];

Random randGen = new Random();
for (int i = 0; i < randomNumbers.Length; i++)
{
    randomNumbers[i] = randGen.Next(0, 100);
}

bool found = false;
for (int i = 0; i < randomNumbers.Length; i++)
{
    if (randomNumbers[i] > 50 && randomNumbers[i] < 60)
    {
        found = true;
        break;
    }
}

Console.WriteLine($"Number between 50 and 60{(found ? "" : " NOT")} FOUND");
Console.WriteLine("Application closing");

Switch goto

The goto statement can also be used inside a switch statement, to jump to any of the other switch cases. The switch case label can be used in the same was as a label in the above example.

In this example, the price of a service is determined by the service type, which will adjust the base price accordingly:

public enum ServiceType
{
    Basic,
    Premium,
    UltraFast,
    Enterprise
}

public int CalculatePrice(ServiceType serviceType)
{
    int price = 0;

    switch (serviceType)
    {
        case ServiceType.Basic:
            price += 10;
            break;

        case ServiceType.Premium:
            price += 10;
            goto case ServiceType.Basic;

        case ServiceType.UltraFast:
            price += 20;
            goto case ServiceType.Premium;

        case ServiceType.Enterprise:
            price += 10;
            goto case ServiceType.Premium;
    }

    return price;
}

As you can see, the goto case is used to just from one switch case to another, using the switch case label, adjusting the price as required.

Notes

The goto statement should almost never be used, or be required to be used - however in the small niche uses cases where it is required, an understanding of how and when it can be used will be essential.

References

The goto statement
"goto" statement should not be used

Daily Drop 59: 25-04-2022

At the start of 2022 I set myself the goal of learning one new coding related piece of knowledge a day.
It could be anything - some.NET / C# functionality I wasn't aware of, a design practice, a cool new coding technique, or just something I find interesting. It could be something I knew at one point but had forgotten, or something completely new, which I may or may never actually use.

The Daily Drop is a record of these pieces of knowledge - writing about and summarizing them helps re-enforce the information for myself, as well as potentially helps others learn something new as well.