rookie

hi,
im a rookie in excel, and hope that you experts can help me in solving this problem i'm facing right now.

I have to calculate something using a very long algorithm. Anyway, the point is I want to see how the result changes with the change of one input variable. So, I only need to give a number as an, say, initial value, and variate this value (for maybe 50 to 100 times) and see how the result changes by drawing a curve between the input and the result. The variation is simply the 5%-bigger and smaller number of my initial value.

So, my question is, how can I make a loop using such a 'for' function in excel, to be able to do the calculation many times for different input? so that after I gave the initial value, I can have 2 rows containing my variation of the variable input, and the result for each value.

thanks a lot, even only for reading.. but answers and solutions are very much expected..! please..