Simple While Loop
The While statement is one of the basic programming concepts. It repeatedly executes the piece of code.
Imagine you have a task: write the code to calculate the factorial of the given number. For example, for n = 6 the result is: res = 1*2*3*4*5*6 = 720.
The step by step solution is:
n = 6:
res = 1
res = res * 2 = 2
res = res * 3 = 6
res = res * 4 = 24
res = res * 5 = 120
res = res * 6 = 720
Each operation is a new line of code. How many lines are needed? For huge numbers, you'll get very long instructions.
Instead, we'll use the loops. Take a look at how it works:
There are two main parts: stop condition and body. Body are instructions that need to be executed several times. For the factorial task, the body is multiplication the res by the next number. The condition helps to know when to stop.
If a condition is True, the body is executed one more time. When the condition becomes False, the loop is over and we leave it.
In the factorial task, we multiply all numbers from 1 to n so the loop is over when the multiplier becomes greater than n. This way, the stop condition must be False when it happens and True otherwise.
Here is what the syntax looks like in Python:
12while condition: instructions
Let's code the factorial task in Python. The body instructions are two lines of code:
- basic operations like multiplying the result by the new number.
- counter change.
1234567n = 6 i = 1 # counter res = 1 # result variable while i<=n: res *= i i += 1 print(i, res)
i is a multiplier which takes all values from 1 to n. It increments by 1 on each iteration. The stop condition is i<=n which is True at the beginning and becomes False when i==n+1. After that, the instructions are over, and the values of i and res are displayed in the console. Now i == n+1.
Swipe to start coding
The task is to find all positive numbers that are multiples of 3 less than 20. We'll do that using loops: starting with num = 0 (0 is a multiple of 3), insert num into the list numbers and then increment the num by 3. Insert the next value and so on until num <= 20.
Output the values in the numbers list.
Oplossing
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The While statement is one of the basic programming concepts. It repeatedly executes the piece of code.
Imagine you have a task: write the code to calculate the factorial of the given number. For example, for n = 6 the result is: res = 1*2*3*4*5*6 = 720.
The step by step solution is:
n = 6:
res = 1
res = res * 2 = 2
res = res * 3 = 6
res = res * 4 = 24
res = res * 5 = 120
res = res * 6 = 720
Each operation is a new line of code. How many lines are needed? For huge numbers, you'll get very long instructions.
Instead, we'll use the loops. Take a look at how it works:
There are two main parts: stop condition and body. Body are instructions that need to be executed several times. For the factorial task, the body is multiplication the res by the next number. The condition helps to know when to stop.
If a condition is True, the body is executed one more time. When the condition becomes False, the loop is over and we leave it.
In the factorial task, we multiply all numbers from 1 to n so the loop is over when the multiplier becomes greater than n. This way, the stop condition must be False when it happens and True otherwise.
Here is what the syntax looks like in Python:
12while condition: instructions
Let's code the factorial task in Python. The body instructions are two lines of code:
- basic operations like multiplying the result by the new number.
- counter change.
1234567n = 6 i = 1 # counter res = 1 # result variable while i<=n: res *= i i += 1 print(i, res)
i is a multiplier which takes all values from 1 to n. It increments by 1 on each iteration. The stop condition is i<=n which is True at the beginning and becomes False when i==n+1. After that, the instructions are over, and the values of i and res are displayed in the console. Now i == n+1.
Swipe to start coding
The task is to find all positive numbers that are multiples of 3 less than 20. We'll do that using loops: starting with num = 0 (0 is a multiple of 3), insert num into the list numbers and then increment the num by 3. Insert the next value and so on until num <= 20.
Output the values in the numbers list.
Oplossing
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