Loops with Ranges

The range as a sequence with .. and ...

The range is used to generate a sequence of values. It requires a start point and an endpoint to specify the values. There are two kinds of ranges:

1. The range specified with .. generates the values, including the upper limit. For example, 0..100 generates values $0$ to $100$.

2. The range specified with ... generates the values excluding the upper limit. For example, 0...100 generates values $0$ to $99$.

It also makes it easy to specify the increment or jump value using the step function. For example, 10..100.step(2) generates even values between $10$ and $100$.

Loop with .. and ...

Let’s say we want to produce a program that counts from $1$ to $100$. One way to do this is with the help of a range, as follows:

The 1..100 sequence produces integers from $1$ to $100$. It works exactly the same as listing these values in square brackets separated by commas.

Let’s take another example of generating the first $100$ non-negative even numbers: $0$, $2$, $4$ $...$ $198$.

In this program, ... generates values from $0$ to $99$, and we multiply each value by $2$, which displays 0*2, 1*2, 2*2 … 99*2.

We may generate even numbers with the same sequence as above using the built-in step function with .... We can directly use the (0...100).step(2), as shown in the following program:

If we want to generate the multiples of 7 between 1 and 700, we can use (7...701).step(7). We use 7 as starting value so that every increment of 7 may take us to the next multiple of 7. Incorporating this in the for loop will allow us to show the generated values as output.

Programming practice for .. and ... in loops

The following are a few examples to help you practice writing the programs in Ruby using the range. By clicking the “Show Solution” button, you’ll find the program that solves the respective problem. You may copy and paste the given solution into the code widget to make sure your solution matches the given solution. There can be several ways to write correct solutions in programming.

Odd numbers

Write a program that prints the first 100 positive odd numbers $1,3,5 ... 199$.

Arithmetic sequence

Write a program that prints the terms of the sequence $1, 6, 11 ... < 100$.

Table of $n$

Write a program that takes an integer input by the user and prints a multiplication table for the first 20 multiples, as illustrated below:

Sample input

5

Sample output

5 x 1 = 5

5 x 2 = 10

.

.

.

5 x 20 = 100

Mean of $n$ inputs

Write a program that calculates the average of the numbers input by the user. The program first asks the user how many values they want to average. The number of values should be greater than $0$.

Sample input

4
10
20
30
40

Sample output

The average is : 25

Factors of user input

Write a program that shows all the factors of a number provided by the user.

Sample input

20

Sample output

1
2
4
5
10
20

Prime or not

A prime number is divisible only by itself and $1$.

Write a program that shows whether or not the natural number input by the user is a prime number.

Sample input 1

7

Sample output 1

7 is a prime number

Sample input 2

20

Sample output 2

20 is not a prime number