Transcript Quest Review: Loops

Quest Review 1: Loops
While Loop
• Mr. Tan gives you an array, randIntsForTan,
with random integers in it. You need to tell
him the sum of all the even integers in the
array. You decide to write a while loop to
accomplish this.
• Write the while loop that will find the sum of
all the even integers in the array.
While Loop
int sum = 0;
int index = 0;
while(index<randIntsForTan.length) {
if (randIntsForTan[index]%2==0) {
sum += randIntsForTan[index];
}
index++;
}
For Loop
• Mr. Tan is happy that you wrote such a wellwritten while loop, but was expecting that you
would write a for loop instead since they are
faster to write than while loops.
• Change the while loop that you just wrote into
a for loop.
For Loop
int sum = 0;
for(int i= 0; i<randIntsForTan.length, i++) {
if (randIntsForTan[i]%2==0) {
sum += randIntsForTan[i];
}
}
For-Each Loop
• Mr. Tan is pleased that you know how to
convert while loops into for loops so easily,
but would like to also make sure that you can
use the for-each loops.
• Convert your for loops into for-each loops to
prove to him that you know your stuff.
For-Each Loop
int sum = 0;
for(int num : randIntsForTan) {
if (num%2==0) {
sum += num;
}
}
Array Loops
• The following program segment is intended to
find the index of the first negative integer in
arr[0]…arr[N-1], where arr is an array of N
integers. Will it work? When will it work?
int i = 0;
while(arr[i] >= 0) {
i++;
}
location = i;
Array Loops
• Needs at least one negative integer
• Change to:
int i = 0;
while(i<arr.length) {
if (arr[i] < 0) {
break;
}
i++;
}
location = i;
Array Loops
• Consider the following code segment:
int sum = arr[0];
int i = 0;
while(i < arr.length) {
i++;
sum += arr[i];
}
What is the result of executing the segment?
Array Loops
• How would you rewrite the while loop?
int sum = arr[0];
int i = 0;
while(i < arr.length) {
i++;
sum += arr[i];
}
• How about as a for loop? For each loop?
Array Loops
• The following code fragment is intended to find the
smallest value in arr[0]…arr[n-1]
int min = arr[0];
int i = 1;
while(i<n) {
i++;
if (arr[i] < min) {
min = arr[i];
}
}
What changes need to be made?
Array Loops
Array arr1 contains elements arr1[0]…arr1[N-1],
where N is arr1.length
int count = 0;
int[] arr2 = new int[count];
for (int i = 0; i<N; i++) {
for(int i = 0; i<count; i++) {
if (arr1[i] != 0) {
arr2[i] = arr1[i];
arr1[count] = arr1[i];
}
count++;
}
If array arr1 initially contains the elements
}
0, 6, 0, 4, 0, 0, 2 in this order, what will arr2
contain after execution of the code segment?
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•
•
•
•
0, 6, 0, 4, 0, 0, 2
 6, 6, 0, 4, 0, 0, 2
 6, 4, 0, 4, 0, 0, 2
 6, 4, 2, 4, 0, 0, 2
arr2  6, 4, 2