Calculate the sum of odd numbers greater than 9 and less than 30 a for-loop .
Solution
Explanation
To accomplish our task, we should remember challenge #02 because back then, the task was to print out every odd number below 99. That means we create a for loop with an increment of 2 after each iteration to get only odd numbers when starting with an odd number. In our case with 11.
Remembering challenge #05 makes us also happy again. There we had the task to create the sum of the numbers from 1 to 24. The same concept applies to this task. We add up every odd number above 9 and below 30 to a sum.
After the loop has finished, we print it out to the console:
Accumulated value printed out to the console (Sum of all odd numbers >9 & <30)
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To create the factorial of 9 we make almost the same as in challenge #05 but with a different loop body code block.
Last time we used this statement to gather the accumulated sum sum+=i. Knowing a bit about mathematics means you are aware of the fact that a factorial is nothing more than a chained multiplication.
So 9! is nothing more than 9*8*7*6*5*4*3*2*1. Together with the knowledge about for-loops we can draw advantages out of this by using the running index of i to create a factorial. To get our desired result, we iterate exact 9 times!
Result of 9! printed out to the console
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Calculate the sum of numbers from 1 to 24 with a for-loop .
Solution
Explanation
For diversity, another challenge, but a simpler one! But that doesn’t mean you can switch off your brain 😉
We can’t just put the accumulated value of sum inside the loop and print it to the console. It would then end up with 24 print outs.
We have to declare and initialize the variable (and please use let here! You can read about the problems of declaring variables with var, let, and const in the featured article below. I advise you to do so!) outside of the loop in order to print it out afterward.
Declaring the variable inside the loop, then it would be initialized every iteration, instead of holding the actual accumulated value.
Furthermore, if we declared it inside the loop it would be out of our reach when we want to access it outside the loop. This is called a scope, declaring a variable inside a class/function/loop, makes it to a local variable which can’t be accessed from the outside (The article below addresses this in detail).
And this is the console output:
Console Printout of the solution.
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