CS50 Week 3

Question 1

What happens if you try to access an element beyond the bounds of an array?

Answer 1

A segmentation fault

Question 2

What function will convert a char to a value?

Answer 2

atoi(s)

Question 3

What is a simple but effective debugging technique?

Answer 3

printf()

Question 4

What is the clang argument that allows for gdb debugging?

Answer 4

-ggdb3

Question 5

After compiling, how do you open GDP?

Answer 5

gdb debug

where debug is the name of the program being debugged.

Question 6

What is a breakpoint in gdb?

Answer 6

A point at which the program pauses executing

Question 7

Where is a convenient place to put the first breakpoint?

Answer 7

main()

Question 8

How do you step line by line through your code in gdb?

Answer 8

next

Question 9

How do you reenter the last command you typed?

Answer 9

hit enter with no command.

Question 10

How do you start your program running from within gdb?

Answer 10

run

Question 11

How do you check the value of a variable at the point that you are in the code, while within gdb?

Answer 11

print i

where i is the name of the variable

Question 12

How do you display the code before and after your current position?

Answer 12

list

Question 13

How do you move execution by execution within a function call, using gdb? This is distinct from the command “next”

Answer 13

step

step will be distinct from next only if you are at a function call, in which case it will follow the function instead of going to the next line of code in the sequence.

Question 14

How do you set a breakpoint in gdb

Answer 14

break functionName

Question 15

What is a linear algorithm?

Answer 15

An algorithm of n complexity.

It will execute n times where n is the size of the input.

Question 16

What is a logarithmic algorithm?

Answer 16

An algorithm of log(n) complexity.

It will execute log(n) number of times, where n is the size of the input.

Question 17

What is bubble sort?

Answer 17

A sorting technique that starts at the first two values of a non-sorted sequence and compares them. If the numbers are out of order, it swaps the first and second values. Then it compares the second and third values, and does the same. It does this until the entire sequence can be read with no swaps.

Question 18

What is the complexity of bubble sort?

Answer 18

n^2

Question 19

What is selection sort?

Answer 19

The algorithm reads each value in a non-sorted sequence and remembers the smallest number. It then swaps the smallest number with the first number in the sequence. It then repeats this process on the unsorted elements of the sequence until all are sorted.

Question 20

What is the complexity of selection sort?

Answer 20

(n(n-1))/2

This ends up being very close to n^2, so we say n^2

Question 21

What is insertion sort?

Answer 21

An algorithm that sorts the elements in place. It examines each element in a non-sorted list, and places it in the appropriate position in a sorted list.

Question 22

What is the complexity of insertion sort?

Answer 22

n^2

Question 23

What is the best case scenario for bubble sort?

Answer 23

n

Question 24

What is the best case scenario for selection sort?

Answer 24

n^2

Question 25

What is the worst case scenario for linear search?

Answer 25

n

Question 26

What is the worst case scenario for binary search?

Answer 26

log(n)

Question 27

What is the best case scenario for binary search?

Answer 27

1

Question 28

What is the best case scenario for linear search?

Answer 28

1

Question 29

In GDB, how do you display the active variables?

Answer 29

info locals

Question 30

How do you deactivate a breakpoint in GDB

Answer 30

disable

Question 31

How do you tell GDB to finish running the program, without going line by line?

Answer 31

continue