Mike is right, your algorithm for finding the largest number in an array is not quite right.
Here are some guidelines that will help you come up with a better approach:
1. You may only iterate through the entire array once.
2. You may only look at one array element at a time (your current algorithm looks at two elements on each iteration).
3. Besides the array and (possibly) a loop index, you may use only one other variable in your algorithm
Imagine solving this problem with real-world objects. The array is a row of boxes, each filled with an unknown random number of marbles. You are asked to find out what is the most number of marbles in any of the boxes. Basically the same rules apply: you may only count the marbles in one box at a time. When you're done with a box, you may never look at it again. You are not allowed to memorize or remember anything about a box or its contents after you are done looking at it. The only "memory device" you are allowed to use is a small notepad. You are given a pencil which has an eraser so you can erase your current note before jotting down a new note.
Given these rules, what is the most straightforward way you can think of to figure out the most number of marbles in any of the boxes.