Presenting the concepts of pointers and arrays in C

1. Pointers and Arrays
4th session

2. Example
Suggest three different ways
to make an infinite loop
which way is the best ?!
Get your hands dirty

3. Think OF
Swap Function

4. void swap(int a, int b)
{
int tmp = a;
a = b;
b = tmp;
}

5. Pointers

6. Memory

7. int main(void)
{
int *x;
int *y;
x = malloc(sizeof(int));
*x = 42;
*y = 13;
y = x;
*y = 13;
}

8. int main(void)
{
int *x;
int *y;
x = malloc(sizeof(int));
*x = 42;
*y = 13;
y = x;
*y = 13;
}

9. int main(void)
{
int *x;
int *y;
x = malloc(sizeof(int));
*x = 42;
*y = 13;
y = x;
*y = 13;
}

10. int main(void)
{
int *x;
int *y;
x = malloc(sizeof(int));
*x = 42;
*y = 13;
y = x;
*y = 13;
}

11. int main(void)
{
int *x;
int *y;
x = malloc(sizeof(int));
*x = 42;
*y = 13;
y = x;
*y = 13;
}

12. int main(void)
{
int *x;
int *y;
x = malloc(sizeof(int));
*x = 42;
// *y = 13;
y = x;
*y = 13;
}

14. Pointers
• Variable whose value is a memory address
• Pointers are represented internally as unsigned int on most
systems
• %p (ANSI C)

15. Pointer Fun
https://www.youtube.com/watch?v=5VnDaHBi8dM

16. void swap(int a, int b)
{
int tmp = a;
a = b;
b = tmp;
}

17. void swap(int *a, int *b)
{
int tmp = *a;
*a = *b;
*b = tmp;
}

18. Think oF
scanf("%d", &x)

19. why?
<data type> *ptr = <address>

20. Referencing and dereferencing
referencing :
&<variable name>
dereferencing:
*<pointer name>

21. Variables VS Pointers

22. Arrays

23. Arrays
• Series of elements of one data type
• int grades[50];
• student[index] = 85;

24. Arrays Initialization
• int arr[4] = {11, 2, 4, 6};
• int arr[4];
• int arr[4] = {11, 2}; // " The rest are Zeros "
• int arr[ ] = {11, 2, 4, 6};
• int arr[150] = {[48] = 2, 4}; // " The rest are Zeros " C99
• int arr[ ] = {2, [7] = 3, 9};

25. How to get the size of an array

26. sizeof(array) / sizeof(array[0])

27. Often LOOPS for assigning arrays

28. Make sure you are within bounds

30. Function call
All this data is pushed into
the stack when calling

31. Function call
Memory addresses goes
downwards

32. Function call
All this data is pushed into
the stack when calling

33. Specifying an Array Size
• <Data Type> <Array Name>[int literal];
• int arr[<variable>]; //Not allowed before C99

34. Multidimensional Arrays

35. Two-dimensional Arrays
• double x[5] [7];
• An array of arrays
• int arr[2][3] = {
{ 1, 3, 5 },
{ 4, 7, 8 }
}

36. Arrays and Pointers

37. Pointers and Arrays
• Pointers and arrays are tightly coupled
• An array name is actually the address of the first element of the
array
• *(arr + i) is what is really happening

39. Functions with Arrays as inputs

40. Pointer Operations
• Assignment
• referencing and dereferencing
• Adding, subtracting an int , increment and decrement
• &ptr
• (ptr1 - ptr2)
• Comparisons

41. Cautions
• Exceeding the array boundary
• Dereferencing an uninitialized pointer

42. Pointer Arithmetic

44. Protecting Data Passed to Functions

46. Complicated Declarations
• int *arr [ ] ;
• float rain [5] [12];
• const double *p;
• double * const p;
• const double * const p;

47. Pointer to constants
Vs
Constant Pointers

48. Pointers and Const
• Only The addresses of non-constant data can be assigned to
regular pointers
• with const you can create a pointer to constant, a constant
pointer and a constant pointer to constant

50. Thanks !