CS50 Week 5

Question 1

a hexadecimal memory address is prefixes with what?

Answer 1

0x

Question 2

What is the base number for hexadecimal, and what symbols are used?

Answer 2

Base 16

0-9 and A-F

Question 3

What does == compare for pointers?

Answer 3

The memory addresses, not the content of those addresses.

This is especially important when comparing strings.

Question 4

How are pointers often represented in pseudocode?

Answer 4

As arrows.

Question 5

What is the easiest way to compare strings?

Answer 5

the functions strcmp( )

Question 6

What are two causes of segmentation faults?

Answer 6

Iterating past the bounds of an array.

Dereferencing a pointer that hasn’t been initialized.

Question 7

What information exists in memory before it is initialized?

Answer 7

Who know!? It is just a garbage value before you put something there.

Question 8

In what way is an array a pointer?

Answer 8

An array is a pointer with a different syntax than using a *. The two are the same thing.

• c is equivalent to c[0]
• (c+i) is equivalent to c[i]

Question 9

Visualize a graphical representation of memory:

Answer 9

text
----------------
initialized data
------------------
uninitialized data
--------------------
       heap
          |
         V

        ^
         |
     stack
----------------------------
environmental variables

Question 10

What are the four steps of compiling?

Answer 10

pre-processing

compiling

assembling

linking

Question 11

What happens during pre-processing?

Answer 11

The header files are pasted to the top of the program, and constants in the body are replaced with their values.

Question 12

What happens during the compiling phase?

Answer 12

The source code is translated into assembly language.

Question 13

What happens during assembling?

Answer 13

The assembly language is translated into machine code.

Question 14

What happens during linking?

Answer 14

The machine code is combined with whatever other machine code has been specified.

Question 15

What is in the “text” portion of the memory diagram?

Answer 15

The 0s and 1s of the program.

Question 16

What is in the initialized data and uninitialized data portions of the memory diagram?

Answer 16

global variables.

Question 17

What is the danger of not checking the bounds of our arrays?

Answer 17

A stack overflow or buffer overrun attack.

Question 18

What happens when if the stack runs into the heap?

Answer 18

A segmentation fault.

Question 19

What is the tool for finding memory leaks?

Answer 19

Valgrind

Question 20

What is a memory leak?

Answer 20

Memory that has been allocated to the heap that is never freed.

Question 21

What is the command to start Valgrind

Answer 21

Valgrind ./file-name

Question 22

What is the command-line argument for a more detailed description by Valgrind?

Answer 22

–leak-check-full

Question 23

Valgrind can also detect some errors where an array is overstepped.

Answer 23

Valgrind can also detect some errors where an array is overstepped.

Question 24

What does typedef do?

Answer 24

It creates an alias for a type.

Question 25

What is a sentinel value?

Answer 25

A value that is returned when a program doesn’t work correctly.

Question 26

What is the format for sscanf()?

Answer 26

sscanf(characterArray, “Conversion specifier”, address of variables);

Question 27

What does struct do?

Answer 27

It creates a new data structure.

Question 28

What is the format for a struct?

Answer 28

struct name
{
data housed = data;
}

Question 29

How would a struct be given a new name?

Answer 29

typedef struct x
{
    data;
}
name;

Question 30

How do you access a variable inside a struct?

Answer 30

with . notation. Example?

typedef student
{
    char* name;
}
student;

student prime;
prime.name = “James”;