Variables and control flow

In plain English

A variable names a value the program can change, and its type tells the compiler what that value can do. var lets the compiler infer the type, while an explicit type like int documents your intent. if and else choose between two paths, and a switch expression picks one result from many cases. Loops such as for, foreach and while repeat code, and scope decides where a variable is visible.

Step by step

1. 1Declare a string and an inferred var, then print both.
2. 2Branch with if/else and add a switch expression.
3. 3Repeat with for and foreach loops.
4. 4Move a variable into a narrower scope and watch it go out of reach.

string title = "C# Foundations";
var minutes = 12;

if (minutes > 10)
{
    Console.WriteLine(title + " is a long lesson");
}
else
{
    Console.WriteLine(title + " is a short lesson");
}

var label = minutes switch
{
    <= 10 => "short",
    <= 20 => "medium",
    _ => "long",
};
Console.WriteLine(label);

for (var i = 0; i < 3; i++)
{
    Console.Write(".");
}
Console.WriteLine();

foreach (var word in title.Split(' '))
{
    Console.WriteLine(word);
}

Common mistakes

• Redeclaring the same variable name in the same scope causes a compile error.
• Comparing strings with == instead of Equals can surprise you when case matters.
• Putting a variable in a wide scope invites accidental reuse and bugs.
• Off-by-one loop bounds either skip the last item or run once too many.