## CS 1401, Quiz 10, Solutions

**Date:** Tuesday, April 3, 2007

**Name** (please type
legibly, ideally in block letters):
______________________________________________________________________

**Class section** (9:00 am or 10:30 am):
_______________________________
1. Write a piece of code that, given an array *ar* of integers,
computes the largest element of this array.

Solution:
int largestSoFar = ar[0];
for (int i = 1; i < ar.length; i++)
{if (ar[i] > largestSoFar) largestSoFar = ar[i];}

2. To check the correctness of the code you wrote in Problem 1,
write a piece of code that defines a new array *ar* consisting
of 2 elements of type integer and assigns, to elements of this
array, values 1 and 2. Trace step-by-step how the piece of code you
wrote in Problem 1 will compute the largest element of this array.

Solution:
int[] ar = {1, 2};
Tracing:
The fact that we have defined an array ar with 2 elements means, in
effect, that we have defined two variables ar[0] and ar[1]:
----
| \|
---\
ar \
\|
- -------
| 1 | ar[0]
-------
| 2 | ar[1]
-------
Then, we define a new variable largestSoFar and assigning to it a value 1:
-------
| 1 |
-------
largestSoFar
Next, we get to the for-loop. First, we define a new integer variable
i and assign to it the value 1:
------- -------
| 1 | | 1 |
------- -------
largestSoFar i
We check the condition: the length of our array ar is 2, so i is smaller
than this length. Thus, the condition i < ar.length is satisfied, and
we implement the operation in the body of the loop. Since i = 1,
we check the condition ar[1] > largestSoFar, i.e., 2 > 1. This
condition is satisfied, so we replace the previous value of largestSoFar
with a new value 2:
------- -------
| 2 | | 1 |
------- -------
largestSoFar i
Then, we go to the update statement i++; this statement adds 1 to i, so
we get:
------- -------
| 1 | | 2 |
------- -------
largestSoFar i
The condition i < ar.length is no longer satisfied, so we stop.