week 2 c programming code

Question 1

what is a string in c#

Answer 1

string of characters is a 1D array of characters

Question 2

how much memory does ASCII store

Answer 2

(1 byte) of each character element is stored in
consecutive memory locations

Question 3

what is string terminated by

Answer 3

String is terminated by the null character ‘\0’ (ASCII value 0)

Question 4

what is the length of the null string

Answer 4

The null string (length zero) is the null character only

Question 5

what is use to take input from user in c#

Answer 5

scanf()

Question 6

what is used to output info to user

Answer 6

printf()

Question 7

what is the format for string in c

Answer 7

%s

Question 8

what is the 4 safe string functions

Answer 8

strcpy()
strcat()
strlen()
strcmp

Question 9

what is strcpy()

Answer 9

copies the string from one destination to another

Question 10

what do you need to make sure that you do in strcpy()

Answer 10

need to allocate memory to the destination where you want to put your string
e.g
char[10] destination; -> where i will put the string in;

Question 11

what does strlen do

Answer 11

gets the length of the string;

Question 12

does strlen take into account the null value

Answer 12

no

Question 13

what does strcat do

Answer 13

concatenates 2 strings together

Question 14

in strcat(str1,str2) which string is modified and which stays the same

Answer 14

str2 stays the same and str1 changes as str2 is appended to teh end of str1

Question 15

what does strcmp do

Answer 15

compares 2 strings and see if they are the same

Question 16

if strcmp conpares 2 strings and finds them to be equal then what does it return

Answer 16

it returns 0

Question 17

if strcmp conpares 2 strings and finds them to not be equal then what does it return

Answer 17

returns the numeric difference between the first
non matching characters
or -1 i need to check

Question 18

what are string problems

Answer 18

Need to ensure that sufficient memory is allocated at run-
time for storing the string - not automatically done by the
compiler

• No checks at run-time (and compile-time), hence common
  source of errors
• Such “buffer overflows” have been exploited to achieve
  execution of code supplied by attackers
• Partial solution is to use “safe” functions

Question 19

what is a partial solution to string problems

Answer 19

• Partial solution is to use “safe” functions

Question 20

what are safe string functions

Answer 20

strcpy() strcmp , strlen , strcat

Question 21

what is wrong with this
strncpy(char *dst, char * src, size_t num)

Answer 21

Copies the first num characters of src to dst. If the end of src
(signaled by a null char) is found before num characters have been
copied, dst is padded with zeros until a total of num characters
have been written to it.

No null-character is implicitly appended at the end of dst if src is
longer than num. Thus, in this case, dst shall not be considered a
null terminated C string

Question 22

what is the definition of a pointer

Answer 22

A pointer is a variable that contains the address of a
variable
pointer is also stored in memory

Question 23

what is the unary operator*

Answer 23

• is also calld indirection or dereferencing operator
  applied to a pointer to accesses the object the pointer points to
  e.g c = 5 , *p = &c , d = p now d = 5

Question 24

what is unary operator &

Answer 24

‘address-of’ operator
points to address of object
p =&c
now p now has address of c so p points to c

Question 25

how to declare a pointer in C#

Answer 25

T *p T is any data type like int or char

Question 26

does string exists in c#

Answer 26

no string does not exists we use char[] instead

Question 27

do & and * have a higher precedence then arithmetic operations

Answer 27

yes

Question 28

can pointers appear in expressions?

Answer 28

* Pointer variables can appear in expressions * If ‘p’ points to the object ‘x’, then *p can occur in any context

Question 29

can a pointer variable be assigned to another pointer variable of the same type?

Answer 29

yes , a pointer variable can be assigned to another pointer variable of the same type

Question 30

scale factors in point expressions remind me to change this card

Answer 30

If p is a pointer then p++ or p+1 ➢ points to the next object of the same type. So, ➢ value of p increments by 4 when p is an int pointer ➢ value of p increments by 4 when p is a float pointer ➢ value of p increments by 1 when p is a char pointe

Question 31

what is the syntax to finding out the scale factor in C#

Answer 31

sizeof(data_type)

Question 32

what is the scale factor in C

Answer 32

number of bytes used by a data-type

Question 33

what can i use to find scale factor in C

Answer 33

sizeof()

Question 34

how many bytes in int char float *int *char *float

Answer 34

int - 4 char - 1 float - 4 *int - 8 *char - 8 *float -8

Question 35

what is an array in C

Answer 35

sequential collection of elements of the same type

Question 36

how does pointer work in an array in C

Answer 36

int a[10]; int *p = &a[0]; p is a pointer to the first element of array a int b = *p; will copy value of a[0] into b

Question 37

accessing array elements using pointers

Answer 37

If p points to the first element a[0], then * p+1 points to a[1] * p+i points to a[i] So, *(p+i) refers to the content of a[i]

Question 38

what does *(p + i) refer to

Answer 38

refers to the content of a[i] in array

Question 39

write for loop to compute sum of array of integers using pointers

Answer 39

int *p = &a[0]; int sum=0, i; for(i=0; i<5; i++) sum = sum + *(p+i);

Question 40

what is array - name a synonymn of

Answer 40

synonym for the location of the initial element

Question 41

what can int *p = &a[0]; also be written as using array name

Answer 41

int *p = a;

Question 42

write for loop for sum of array of integers using array name and pointers

Answer 42

int sum = 0; for (int i = 0 ; i < a.length ; i ++) { sum = sum + *(a + i); }

Question 43

What is the memory layout of a C program

Answer 43

1) Text or Code segment 2) Data segment 3) stack segment 4) heap segment

Question 44

what is the Text / code segment

Answer 44

Text segment contains the the program i.e. the executable instructions

Question 45

what is the data segment

Answer 45

Two data segments contain initialized and uninitialized global and static variables respectively

Question 46

what is the stack segment

Answer 46

Stack segment is used to store all local or automatic variables. When we pass arguments to a function, they are kept in stack

Question 47

what is the heap segment

Answer 47

Heap segment is used to store dynamically allocated variables are stored

Question 48

what is a static variable

Answer 48

* Static variables are stored in the data segment, not in the stack. * The data segment is active during the entire life-time of program * So, static variables preserve their values even after they are out of their scope.

Question 49

what is a global variable

Answer 49

A global variable is declared outside all functions. * It can be read or updated by all functions. Careful: Do not name any local var in the name of a global var

Question 50

why is using an array not good for a large volume of data

Answer 50

insufficient wasteful tiny computers can not hold large amounts of data

Question 51

what is the solution for dynamci memory allocation

Answer 51

allocate memory at runtime as per demand

Question 52

why is allocating memory at runtime as per demand a good solution

Answer 52

optimal usage of memory depending on current case of applications

Question 53

how can we acces memory aloocation in C

Answer 53

#stdlib.h

Question 54

what syntax can we use for memory allocation in C

Answer 54

malloc(c)

Question 55

what is malloc(c)

Answer 55

allocates requested amount of bytes of contiguous memory from heap returns a pointer of first byte in allocated space or returns null pointer if memory fails

Question 56

what is free(p)

Answer 56

releases dynamically allocated blocks of memory block of memory returns to heap

Question 57

what is something you make sure you do with free() when doing a function

Answer 57

use free() before finishing requests all malloc() need to use free()

Question 58

how to avoid memory leaks in C

Answer 58

always use a free() after you have used a malloc()

Question 59

what happens when there is a memory leak

Answer 59

blocks of memory not returned to heap so program grows larger over time

Question 60

what are the consequences of a memory leak in C

Answer 60

- leaks slow down system preformance as they reduce the amount of available memory - modern applications ystems -> releases memory used by applications when application terminates - memory leaks causes serious issues on resource constrained embedded devices

Question 61

what happens when free() is called twice for the same address and what is the consequence.

Answer 61

if called twice for same address program's memory management becomes corrupt con: prog malfunctions including security vuneralbilities

Question 62

what is a linked list in C

Answer 62

- collection of data elements called nodes, -> search nodes points to next nodes in a list -> not stored in contiguous locations like arrays -> linked using pointers

Question 63

implementations of singly linked list in C

Answer 63

1) append elements at end of the list 2) search for elements in list 3) print , gives start of list 4) free memory is occupied by list

Question 64

what do nodes consist of in C

Answer 64

data reference to the next node ( pointer -> )

Question 65

what data type is node in C

Answer 65

composite data type

Question 66

what is Null in a linked list

Answer 66

end of a list

Question 67

instead of class , what do we use in c

Answer 67

we use structure in C

Question 68

what is Structure in C

Answer 68

User defined composite data type in C Use to deinfed items of possibly different data type into one single data type no member functions

Question 69

what is syntax of structure

Answer 69

struct{ T a; T b; }

Question 70

can you write struct{} in code

Answer 70

struct{ int x; int y; } int main() { struct point p1; }

Question 71

what is an alternative version to using struct{}

Answer 71

typedef struct var{ T a; T b; } v; v -> variable name that we call in other functions

Question 72

how are structure members accessed in different functions

Answer 72

using the dot (.) operator e.g Point p1; p1.x = 1;

Question 73

give example of using typedef for co - ordinates x and Y

Answer 73

typedef struct Point { int x; int y; } point;

Question 74

how are pointers created in structure members

Answer 74

using pointer ( -> ) operator

Question 75

what is "pass by value"

Answer 75

pass data objects to functions as arguments

Question 76

what is "pass by reference "

Answer 76

pass pointers to a function as arguments (no side effects)

Question 77

consequences of using pass - by - value for functions

Answer 77

function gets a local copy of variable fumction only happens within the function and will not be printed out in the main or another function

Question 78

consequences of using pass - by - reference for functions

Answer 78

function gets a local copy of pointer ehich has address of variable pointer update so you get results of the function thst was executed memory locstion is where the variable is stored both function and main can see the result of the variable

Question 79

in a function can pointers be returned

Answer 79

yes they can pointers of the same data type can be returned

Question 80

what one thing you should not return pointers to

Answer 80

do not return pointers to local var do not return address of a variable too