Selection Statements

Selection statements let a program choose one path from several possibilities. Without them, code would only run top to bottom in a straight line.

This is the first major step from “code that executes” to “code that decides.” Real programs constantly ask questions such as:

• Is the input valid?
• Which menu option did the user choose?
• What status is this order in?
• Which branch should run for this type or value?

In C#, the most common selection tools are:

• if
• if / else if / else
• switch statements
• switch expressions

The basic idea

Selection always starts with a question. The answer determines which block runs.

flowchart TD
    A["Start"] --> B{"Evaluate condition or input"}
    B -- First match --> C["Run matching branch"]
    B -- No first match --> D{"Another branch to test?"}
    D -- Yes --> B
    D -- No --> E["Run else or default branch"]
    C --> F["Continue after selection"]
    E --> F

This is why selection code should be read in order. Each branch is an alternative path, not additional work that all runs together.

if statements

Use if when you want to run code only when a boolean condition is true.

int age = 20;

if (age >= 18)
{
    Console.WriteLine("Adult");
}

If the condition is true, the block runs. If it is false, the block is skipped.

This is the most direct form of decision-making in C#.

if / else

Use else when exactly one of two paths should run.

bool isLoggedIn = false;

if (isLoggedIn)
{
    Console.WriteLine("Show dashboard");
}
else
{
    Console.WriteLine("Show login screen");
}

Only one branch runs. That is important. An else block is not a second independent check. It is the fallback path when the if condition is false.

else if chains

Use else if when you need several mutually exclusive choices.

int score = 82;

if (score >= 90)
{
    Console.WriteLine("A");
}
else if (score >= 80)
{
    Console.WriteLine("B");
}
else if (score >= 70)
{
    Console.WriteLine("C");
}
else
{
    Console.WriteLine("Needs improvement");
}

The runtime checks conditions from top to bottom and stops at the first true branch.

That means ordering matters. If you put a broader condition first, later branches may never run.

switch statements

Use a switch statement when you want to select behavior based on one value and several known cases.

string command = "save";

switch (command)
{
    case "open":
        Console.WriteLine("Opening file...");
        break;
    case "save":
        Console.WriteLine("Saving file...");
        break;
    case "exit":
        Console.WriteLine("Closing application...");
        break;
    default:
        Console.WriteLine("Unknown command.");
        break;
}

This is often clearer than a long if/else if chain when each branch depends on the same input.

switch expressions

switch expressions are a more compact form that return a value.

int month = 3;

string quarter = month switch
{
    1 or 2 or 3 => "Q1",
    4 or 5 or 6 => "Q2",
    7 or 8 or 9 => "Q3",
    10 or 11 or 12 => "Q4",
    _ => "Invalid month"
};

This is especially useful when you are transforming one value into another.

When to use which form

• Use if when the condition is a general boolean test.
• Use if / else when there are two clear alternatives.
• Use else if when order matters and you are checking several conditions.
• Use switch when one input is being compared against a known set of cases.
• Use a switch expression when you want to compute and return a value cleanly.

A worked example

Imagine a checkout system that chooses shipping cost based on order amount and delivery speed.

decimal orderTotal = 85m;
string shippingSpeed = "Express";

decimal shippingCost;

if (orderTotal >= 100m)
{
    shippingCost = 0m;
}
else if (shippingSpeed == "Express")
{
    shippingCost = 14.99m;
}
else if (shippingSpeed == "Standard")
{
    shippingCost = 5.99m;
}
else
{
    shippingCost = 9.99m;
}

Console.WriteLine($"Shipping cost: {shippingCost:C}");

Trace it carefully:

1. orderTotal >= 100m is checked first. It is false.
2. shippingSpeed == "Express" is checked next. It is true.
3. shippingCost becomes 14.99m.
4. The rest of the chain is skipped.
5. The final line prints the result.

That “skip the rest after the first match” rule is one of the most important ideas in selection statements.

Common mistakes

• Writing several if statements when only one branch should run. That usually means you wanted else if.
• Ordering conditions incorrectly, which can make later branches unreachable in practice.
• Forgetting a default branch in a switch when unmatched input is possible.
• Using a long if chain where a switch would express intent more clearly.

Summary

Selection statements give your program alternatives.

The main things to remember are:

• if is for conditions
• else is the fallback path
• else if checks multiple alternatives in order
• switch is often clearer when one value chooses among many cases
• switch expressions are excellent when you need to produce a value

Good selection code is not just correct. It is easy to read in the same order the runtime evaluates it.

Practice

Write an if / else if / else chain that prints a description for a temperature: cold, mild, warm, or hot.

As a second exercise, write a switch expression that converts a day number from 1 to 7 into a weekday name.