Chapter 5.1. Loops (Repetitions)

In the present chapter we will get familiar how to repeat blocks of commands, also known in software development as "loops". We will write a number of simple loops using the for operator in its simplest form (for i = 1 … n). Finally, we will solve series of practical problems that require repeating of series of actions, using loops.

Video: Chapter Overview

Watch a video lesson to review what will we learn in this chapter:

Introduction to Simple Loops by Examples

In programming we can execute a block of code multiple times using a simple for-loop like this:

for (int i = 1; i <= 5; i++)

Run the above code example:

The above code prints the numbers 1, 2, ..., 5. The output is as follows:


We can enter multiple numbers from the console and process them using loops like this:

  1. Read the count n of the numbers.
  2. In a for-loop read and process n times one single number.

This is how the above idea may work:

int n = int.Parse(Console.ReadLine());
long sum = 0;
for (int i = 0; i < n; i++)
    int num = int.Parse(Console.ReadLine());
    sum += num;
Console.WriteLine("Sum = {0}", sum);

Run the above code example:

The output from the above example may look like this (when we enter 3 numbers: 10, 20 and 30):

Sum = 60

Let's explain in greater detail how to use simple for loops to repeat blocks of code multiple times in C#.

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