Conditionals

Conditionals decide which code actually runs. C# gives you two main tools for this: if/else for open-ended branching logic, and switch for checking one value against a fixed set of possibilities.

if, else if, else

Conditions are checked top to bottom, and the first one that's true wins — the rest are skipped entirely:

int score = 82;
string grade;

if (score >= 90)
{
    grade = "A";
}
else if (score >= 80)
{
    grade = "B";
}
else if (score >= 70)
{
    grade = "C";
}
else
{
    grade = "F";
}

Console.WriteLine($"Score: {score} -> Grade: {grade}");

Score: 82 -> Grade: B

82 fails the >= 90 check, passes >= 80, and stops there — it never even reaches the >= 70 check. Order matters: if the branches were listed smallest-to-largest instead, every score of 70 or above would incorrectly match the first one it hit.

switch statement

When you're comparing one value against several exact possibilities, a chain of if/else if works but reads repetitively. switch was built for exactly this shape of problem:

int dayNumber = 3;
string dayName;

switch (dayNumber)
{
    case 1:
        dayName = "Monday";
        break;
    case 2:
        dayName = "Tuesday";
        break;
    case 3:
        dayName = "Wednesday";
        break;
    default:
        dayName = "Unknown";
        break;
}

Console.WriteLine(dayName);

Wednesday

Each case needs a break (or another way of exiting, like return) — unlike some languages, C# won't let execution silently fall through from one case into the next by accident; leaving out break where it's needed is a compile error, not a runtime surprise.

switch expressions

Modern C# also has a switch expression — a more compact form that directly produces a value instead of assigning inside every branch. It reads less like a control-flow statement and more like a lookup table:

int dayNumber = 6;

string dayType = dayNumber switch
{
    1 or 2 or 3 or 4 or 5 => "Weekday",
    6 or 7 => "Weekend",
    _ => "Invalid"
};

Console.WriteLine(dayType);

Weekend

The _ at the end is a discard pattern — it matches anything not already covered above it, playing the same role default plays in a classic switch statement. Leave it out and feed the expression a value that matches nothing, and it throws an exception at runtime rather than silently producing nothing.