Computer Science : Computer Science
Study concepts, example questions & explanations for Computer Science
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Example Questions
Example Question #3 : Comparing Run Times
True or False.
The code snippet A has a more efficient running time than code snippet B.
(A)
for (int i = 0; i < 25; i++) {
for (int j = i; j < 25; j++) {
}
}
(B)
for (int i = 0; i < 25; i++ {
for (int j = 0; j < 25; j++) {
}
}
False
True
False
Code snippet A has a running time of O(N2). Code snippet B has a running time of O(N). While the two code snippets may look the same, the second for loop in code snippet A sets j=i. Since j is relying on i, it's multiplying the first for loop's running time by the second for loop's running time. This gives us O(N*N) or just O(N2).
Example Question #271 : Computer Science
for( int i = 0; i < n; ++i){
for( int j = 1; j < n; j *= 2){
someFunction();
}
}
For the code above, what is the run time in Big O notation?
O( log(n) )
None of the above
O( 
O(n log(n) )
O( n )
O(n log(n) )
At first glance we might be tempted to pick O( 
Example Question #272 : Computer Science
BITWISE XOR OPERATION
Given the following binary values
a = 0100 1110
b = 0011 0101
perform an XOR operation (c = a^b). What is the result?
c = 0111 1011
c = 0000 0100
c = 0111 1111
c = 0111 0011
c = 0111 1011
Performing a bitwise excludive OR constitutes in taking both binary values and evaluating as follows: either one or the other (1) never both (0). This is the truth table for a bitwise XOR operation:
Taking both a and b and performing the operation bit by bit we get the following result:
Example Question #273 : Computer Science
True or False.
There is a runtime exception in this code snippet.
int wait_time = 0;
int wait_time = 5;
for (int i = 0; i < wait_time; i++) {
System.out.println(wait_time);
}
False
True
True
Yes, there is a runtime exception in the code snippet. The int wait_time is defined twice which will give a runtime exception. This can be fixed by not declaring int before the second assignment of the variable wait_time.
Example Question #1 : Pre Conditions
USING FUNCTIONS
Consider the following C++ code to perform the following subtraction:
9 - 6:
#include <iostream>
using namespace std;
int main() {
int total = 0;
cout << "This code performs the following math operation: 9 - 6 = ";
total = sub(6,9);
cout << total;
}
int sub(int num1, int num2) {
return (num2 - num1);
}
Is there anything wrong with the code?
The arguments in total should be flipped. Such as: total = sum(9,6);
The code is missing the math library. It should have
#include
The function prototype is missing.
There is nothing wrong with this code.
The function prototype is missing.
Taking a look at each answer, we can see that the order of the arguments passed in the sub function is correct because of the fact that num1 is being subtracted from num2. Also, for simple math operations there isn't a need to include the math library. Lastly, any operation can be done within a function or in main; there is no wrong method however, creating and using functions makes the code in main() easier to read and cleaner.
Now within main(), when the sub() function is called the function has not been defined; meaning that it is not within the scope. This means that we should place the function prototype before main() so that when the function is called, the compiler know that there's a function called sub() that takes in two integer parameters and returns an integer. Therefore this addition will fix our scope issue.
#include <iostream>
using namespace std;
int sub(int num1, int num2); //This addition is the function prototype
int main() {
int total = 0;
cout << "This code performs the following math operation: 9 - 6 = ";
total = sub(6,9);
cout << total;
}
int sub(int num1, int num2) {
return (num2 - num1);
}
Note: Another fix to this issue, is placing the functions right before main(). Although this method is not particularly recommended because it makes main() harder to find, people still use it. The following is an example of fixing the issue by placing the function before main(). Note that the function prototype is not needed when using this method:
#include <iostream>
using namespace std;
int sub(int num1, int num2) {
return (num2 - num1);
}
int main() {
int total = 0;
cout << "This code performs the following math operation: 9 - 6 = ";
total = sub(6,9);
cout << total;
}
Example Question #273 : Computer Science
double square(double n){
return n*n;
}
What MUST be true immediately after the above code snippet has run?
The result will be a positive number.
The result will be stored in a new variable.
It is impossible to tell.
The result will be a negative number.
The value of the input parameter changes.
The result will be a positive number.
Squaring a real number will always produce a positive number. The result does not have to be stored in a new variable; it could be a value that is only needed for a one-off expression, thus, not worthy to be stored in memory. Lastly, since the input was passed by value and not by reference, its initial value will stay the same.
Example Question #1 : Assertions
Which of the following code excerpts would output "10"?
int num = 10;num = (num > 0) ? 11: 12;System.out.println(num);int num = 5;num = (num < 0) ? 10: 11;System.out.println(num);None of the answers are correct.
int num = 5;num = (num > 0) ? 10: 11;System.out.println(num);int num = 5;num = (num > 0) ? 11: 10;System.out.println(num);int num = 5;num = (num > 0) ? 10: 11;System.out.println(num);Each bit of code has something similar to this:
num = (boolean statement) ? X : Y;
The bit at the end with the ? and : is called a ternary operator. A ternary operator is a way of condensing an if-else statement. A ternary operator works like this:
<boolean statement> ? <do this if true> : <do this if false>
The correct answer is
int num = 5;num = (num > 0) ? 10: 11;System.out.println(num);Therefore, the ternary operator portion of code, when converted to an if-else, looks like this:
if (num > 0) {num = 10;else {num = 11;}num is 5, which is greater than 0, it would go into the if, so num would then get 10. Then, num gets printed, which means 10 gets printed (the correct answer).Example Question #42 : Program Analysis
True or False.
The assertion in this code snippet is to prevent users from inputting bad data.
public class UserInput {
int userInput;
public static void main(String[] args) {
assertTrue(isInteger(args[0]));
userInput = args[0];
userInput = 25 - userInput;
}
}
True
False
True
The assertion is used to validate user input. The user is able to input anything into the value at args[0]. Since this is the case, we must validate and make sure that the user is inputting what we want. To make this code snippet better, add error checking to do something if the user did not input an integer.
Example Question #1 : Object Oriented Program Design
Which of the following lines represents a data member?
1. class animal
2. {
3. public:
4. animal();
5. void fetch();
6. private:
7. char bone;
8. }
Line 6
Line 1
Line 7
Line 3
Line 5
Line 7
Data members are variables created in a class, and are typically found under the private: label, as data members are typically kept local to that class. It can be distinguished from member functions because of its lack of parenthesis().
Example Question #2 : Object Oriented Program Design
Which of the following operations allow you to define the function func1() outside of the class definition?
1. class school
2. {
3. public:
4. school();
5. void func1();
6. private:
7. char class;
8. }
=
,
->
::
;
::
The function template for func1() has been defined in the class definition, however the implementation of the function has not. In order to specify what the function does, you must say
classname::functionname()
{
}
Or, in our case,
school::function1()
{
//function definition goes in here
}
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