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: https://youtu.be/GIE2smfXg2g.

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++)
{
    Console.WriteLine(i);
}

Run the above code example: https://repl.it/@nakov/for-loop-1-to-5-csharp.

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

1
2
3
4
5

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: https://repl.it/@nakov/for-loop-sum-n-numbers-csharp.

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

3
10
20
30
Sum = 60

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