One of the hardest things to do when you are a beginner is setting realistic goals for what a "how can I improve"-exercise should contain at your current level.

Hence I would suggest you choose to practice solving small, given exercises, because the ability to finish a program according to a given specification is a very valuable thing for everybody who programs for a living.

I would suggest you have a closer look at http://projecteuler.net/ which has a lot of exercises and an automated "check answer" system, allowing you to work at your own pace. The exercises are well worded, but may require you to think. Some may even require you to think a lot, but even failing to solve those, will teach you something useful.

The full wording of problem 1 is:

If we list all the natural numbers below 10 that are multiples of 3 or 5, we get 3, 5, 6 and 9. The sum of these multiples is 23.

Find the sum of all the multiples of 3 or 5 below 1000.

Do you think you could solve this? Then do it!