C# Loops

Copying the same statement four times works only until the count changes or a correction must be made in every copy. A loop keeps the repeated action in one place and makes the repetition rule explicit. Each pass through the body is called an iteration.

Every terminating loop needs progress toward a stopping condition. The progress may be a counter increasing, input changing, or work being removed from a queue. When neither the condition nor relevant state can change, the loop may never end.

A for header contains initialization, condition, and update. Initialization runs once. The condition is checked before each iteration. If true, the body runs, then the update runs, and the condition is checked again. When false, execution continues after the loop.

In the example, day starts at 1, continues while day <= 3, and increases by one. The sequence is 1, 2, 3. Using day < 3 would stop before 3; using day <= 4 would add one extra iteration. These boundary mistakes are called off-by-one errors.

using System;

class Program
{
  static void Main()
  {
      for (int day = 1; day <= 3; day++)
      {
          Console.WriteLine($"Day {day}");
      }
  }
}

Day 1
Day 2
Day 3

A while loop checks a condition before every iteration. It suits retrying until valid input arrives, processing until no work remains, or simulating until a state is reached. The body may run zero times when the condition starts false.

A do-while checks after the body, so it runs at least once. That can suit a menu that must display before asking whether to continue. It is less common, and while is often easier to reason about because the gate appears first.

int battery = 3;

while (battery > 0)
{
  Console.WriteLine($"Working; charge: {battery}");
  battery--;
}

Console.WriteLine("Battery empty");

Working; charge: 3
Working; charge: 2
Working; charge: 1
Battery empty

When the goal is to process every value in a collection, foreach says that directly. It asks the sequence for each item and assigns the current item to a loop variable. You do not need to manage an index or length, which removes common boundary errors.

A for loop is still useful when position matters, when you need to replace items by index, or when stepping by something other than one. Choose based on what the algorithm needs, not on which syntax is shortest.

string[] cities = { "Karachi", "Riyadh", "Istanbul" };

foreach (string city in cities)
{
  Console.WriteLine(city);
}

break exits the nearest loop immediately. continue skips the rest of the current iteration and starts the next one. They are useful when they express an early decision clearly, such as stopping after a match or ignoring invalid records.

Too many jumps can make a loop hard to trace. First consider whether a better loop condition or a small method would state the rule more directly. Avoid goto in ordinary beginner code; structured loops and methods provide clearer control flow.