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Loop is a program that repeats a set of instructions until it is asked to stop. As an example, we can write a loop program to print out "Hello" 3 times. Loop is a fundamental concept in programming.

Loop must always be given an exit condition. When the condition is met, the loop will stop. If the exit condition is faulty, or doesn't exist. We risk running into an infinite loop scenario. Where the loop will continue to execute the instructions indefinitely. This is usually undesirable.

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Loops, together with conditionals, are used to design control flow. Loops are used to repeat certain tasks. Two main types of loops exist, count controlled loop or condition controlled loop. They both refer to a type of exit condition.

Count controlled loop will repeat instructions based on a number count. Such as 1 to 10. The loop will repeat 10 times, counting from 1 to 10 while doing it.

Condition controlled loop will repeat instructions based on a set condition. Such as "Stop when temperature is above 200 degree celcius?" This could be a program in an electric oven that controls the heating element.

The hardest loop to write is the recursive loop. Which is a concept in functional programming where a function will execute itself over and over again. Like a serpent chasing its own tail.

Many programming languages will offer more than one ways to write loops. In JavaScript, you can write for loop, while loop, recursive loop.

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If I asked you to write a program to calculate the sum of all the numbers between 1 and 20. You will probably write it out like this.

var sum = 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 + 10 + 11 + 12 + 13 + 14 + 15 + 16 + 17 + 18 + 19 + 20;

What if I asked you for the sum between 1 and 1000, are you going to do it the same way? Hopefully not. A simple count controlled loop can help us do that. The following is a simple for loop written in JavaScript. It will add the numbers 1 to 1000 and print out the sum.

var sum = 0;
for (var i = 0; i <= 1000; i++) {
  sum += i;
}
console.log(sum); // It will print 500500

This loop took 0.1 milliseconds to execute in the browser.

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Condition controlled loops are the easiest to run into infinite loop scenarios. It is super important that you take into account all possible edge cases when writing condition loops.

The hardest loop to master is probably recursion. Programmers often rejoice whenever they see an elegant recursive function in use.

Programming

Programming is creating instructions for the computer to perform specific tasks. A person who writes programs is called a programmer. There are many different programming languages a programmer can write programs in.

Variable

A variable is a temporary storage unit in a program. You can think of it as a box. You can use this box to hold an item. You can retrieve the item stored, or swap it with another item.

Conditional

A conditional represents a choice in a program, it dictates what happens next. Such as, if today is a Monday, then make a reservation for dinner with the family, otherwise, eat dinner alone with TV.

Function

A function can be thought of as a machine that performs a specific task. Such as make sandwich. Every time you want a sandwich to be made, you just have to turn on the machine. Or execute the function, as programmers would say.