Pointers - Part 1

Question 1

1 Pass By Value

Answer 1

Func(x, y)
func recieves copies of parameters

Question 2

2 pass by reference

Answer 2

func(&x, &y)
func recieves address to parameter, can change original parameter value

Question 3

3 Local Variable:

Answer 3

only accessible within a specific part of a program

Question 4

4 Automatic Variable

Answer 4

allocates memory upon entering the variable’s block, and automatically un-allocates on exit. only activate/deactivates the memory.

main(){auto int a;} vs func(){int a;}

Question 5

5 Static Variable

Answer 5

Preserves value even if out of scope. doesn’t need to reinitialize in case of new scope.

Question 6

6 String in C

Answer 6

character sequence terminated with null character ‘\0’. stored as array of characters
char str[]=”bob”;
char str[4] = {‘b’, ‘o’, ‘b’, ‘\0’};

Question 7

7 Pointer:

Answer 7

int *pointer = x
pointer == &x //address of x
*pointer == x //value of x

Question 8

8 Dynamic Memory Allocation

Answer 8

Changing data structure size during runtime.
malloc(), calloc(), free(), realloc()
https://www.geeksforgeeks.org/dynamic-memory-allocation-in-c-using-malloc-calloc-free-and-realloc/

does not include local variables; they are assigned automatically by the program within its scope,

dynamic memory allocation is the programmer’s responsibility, including use of free() to avoid loss of data

Question 9

9 Function Arguments

Answer 9

passed parameters to functions, either by value or by referece.
arguments are copied to the program stack at run time, then read by the function

Question 10

10 Dangling Pointer

Answer 10

situation when pointer points to a variable that is out of scope, or the variable’s memory gets deallocated.

use static variables or assign NULL to the pointer to prevent errors

Question 11

11 NULL

Answer 11

C NULL: special reserved pointer value that does not refer to any valid data object

Question 12

12 Interface

Answer 12

collection of functions that describe the bahaviour of an object. program won’t know what to do with them yet, but you can define them later.

struct DrawableInterafce
{
void (* draw)( Object );
void (* rotate)( Object, double );
int (* get_heigth)( Object );
int (* get_width)( Object );
};

https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/interface

Question 13

13 Stack Variable

Answer 13

char *buff[500];

allocating data in stack is easy and fast, but limited, and deleted when you leave the scope. good for small local values.

local variables, arrays

Question 14

14 Data Variable

Answer 14

containers for storing data values.

static, global variables

Question 15

15 Heap “Variable”

Answer 15

char *buff = (char *)malloc(500);

memory used for global variables. supports dynamic memory allocation, but not tightly or automatically managed by the cpu. manually handled by the programmer, slower, and can resize variables (stack variables cannot be resized).

Question 16

16 Array

Answer 16

double balance[5] = {1000.0, 2.0, 3.4, 7.0, 50.0};

collection of variables of the same type

Question 17

17 Array Dynamic Allocation

Answer 17

int* ptr;
int n, i;

// Dynamically allocate memory using malloc()
ptr = (int*)malloc(4 * sizeof(int));

    for (i = 0; i < n; ++i) {
        ptr[i] = i + 1;
    }

Question 18

18 Forward Declaration

Answer 18

void printThisInteger(int);
//code
void printThisInteger(int x) {
printf(“%d\n”, x);
}

declaration of a variable before providing a definition, but tell the compiler to permit use of the variable, but the definition would need to be provided somewhere.

Question 19

Function1 printf

Answer 19

It is used to show output on the screen

printf(“Hello World!”);

Question 20

Function2 scanf

Answer 20

It is used to take input from the user

scanf(“format_specifier”, &variables)

example-

int a;
scanf(“%d”,&a);
printf(“%d”,&a);

Question 21

Function3 sprintf

Answer 21

char str[80];
sprintf(str, “Value of Pi = %f”, M_PI);
puts(str); //prints to terminal

sends formatted output to a string pointed to, by str.

Question 22

Function4 assert

Answer 22

include <assert.h></assert.h>

void assert(int expression);

prints message to stderr and aborts the program if false or 0.

“Assertion failed: expression, file filename, line line-number.”

Question 23

Function 5 malloc

Answer 23

Dynamic Memory Allocation for arrays.

ptr = (int*) malloc(100 * sizeof(int)); //will allocate 400 bytes of memory (100 * 4 bytes), pointer ptr holds the address of the first byte in the allocated memory.

Question 24

Function 6 free

Answer 24

memory allocated with malloc() is not de-allocated automatically, so you need to run free() to remove deallocate memory.

free(ptr);

Question 25

Q1 What is the ILRD convention for function names?

Answer 25

TitleCase, AKA PascalCase

Question 26

Q2 What is the difference between using assert and if on parameters

Answer 26

When if tests false, it either doesn’t run the following block or proceeds to the else block.

Assert will abort the program and print a formatted STDERR

assert(1<0);

Question 27

Q3 What are the escape characters for printf? For scanf?

Answer 27

alert (beep) \a
backslash
backspace \b
carriage return \r
double quote "
formfeed \f
horizontal tab \t
newline \n
null character \0
single quote '
vertical tab \v
question mark \?

\a Beeps the speaker
\b Backspace (moves the cursor back, no erase)
\f Form feed (ejects printer page; may clear the screen on some computers)
\n Newline, like pressing the Enter key
\r Carriage return (moves the cursor to the beginning of the line)
\t Tab
\v Vertical tab (moves the cursor down a line)
\ The backslash character
' The apostrophe
" The double-quote character
\? The question mark
\0 The “null” byte (that’s 0, not the letter O)
\Onn A character value in octal (base 8)
\xnnn A character value in hexadecimal (base 16)

Question 28

Q4 What is a dangling pointer?

Answer 28

situation when pointer points to a variable that is out of scope, or the variable’s memory gets deallocated.

use static variables or assign NULL to the pointer to prevent errors

Question 29

Q5 What will happen if you use a dangling pointer?

Answer 29

you cause a segmentation fault (use free)
also create a core dump file, yay

Question 30

Q6 a What will the following snippet print? b. What will happen if you do not cast ( (unsigned int*)fp; )?

Answer 30

a: type promotion is going to look… weird.
b: 3incompatible type, can’t cast to begin with.

Question 31

Q7 What will the following code print?

Answer 31

33 apparently

Question 32

Q8 What will the following code print?

Answer 32

3

Question 33

Q9 Explain the following:

Answer 33

arr[ ] at location i (3)

array is already a pointer to the address of the first element. dereferencing the array’s address and adding to it will move through the array, and dereferencing the pointers will reveal the elements.

it’s funky, but i[arr] equates to i[int* arr], which equates to *(arr + i)

Question 34

Q10

Answer 34

size 10, int array (or int pointers I suppose..)
character array, size 2
character array of size 2
character array of size 2
character array of size 2?

b.
str1 //lValue of type char, value {a, b}, rather a pointer to a, side effect of accessing the pointer
str2 // lValue array of type char, value being a pointer to letter c in memory
str1=str2 // non-lValue of type char, side effect is a reassignment of str1.

Question 35

Q11

Answer 35

the first will loop 100 times, the second loops 99 times. (++ptr is clalculated to 100 and then checked by the while statement; it equates to arr+100, therefore reaching 100, and will not run for the 100th time.)

Question 36

Q12

Answer 36

Personally, I still prefer array arithmetic,