1. C Programming
Language
By:
Yogendra Pal
yogendra@learnbywatch.com
Dedicated to My mother and Father

2. t
y
Keep your notebook with you.
Write important point and questions that comes in your mind
Solve Mind band exercise.
C
Rewind when not clear
Ask Questions by call or SMS or by mail
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THIS IS POINTERS
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3. Pointer
• Pointer variable
– Contains memory address as their values.
– Normal variable contains a specific value.
– Pointers contain address of a variable.
name
ptr name
a
•
address
1090
9
address
1004
3

4. Pointer…
• Pointer definitions
– * used with pointer variables
int *ptr;
– Defines a pointer to an int (pointer of type int *).
– Can define pointers to any data type.
– Initialize pointers to 0, NULL, or an address
• 0 or NULL – points to nothing (NULL preferred)
• & (address operator)
– Return address of operand
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5. Pointer…
• Initialize a pointer variable with the address of
a variable.
int *ptr , x = 10;
ptr = &x;
ptr x
•
1090
10
1000
Data type of pointer variable & variable must be same.
5

6. Pointer…
• * (indirection/dereferencing) operator
– Returns the value of the corresponding memory
address.
• *ptr and ptr are different variable and hence
has different value.
– ptr is the address of x (1000).
– *ptr is the value at 1000 memory address.
* and & are inverse
6

7. *ptr
ptr x
•
1090
9
10
1000
&ptr ptr
*ptr = 9; y
y = *ptr; 9
1098
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8. Pointer Operators…
Operators Associativity Type
() [] left to right highest
+ - ++ -- ! (type) right to left unary
* &
* / % left to right multiplicative
+ - left to right additive
< <= > >= left to right relational
== != left to right equality
&& left to right logical and
|| left to right logical or
?: right to left conditional
= += -= *= /= %= right to left assignment
, left to right Comma
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9. Pointer and Function
• Call by value
– Pass the value of the variable to the function.
void main() void print(int x)
{ {
10
int x = 10; x += 10;
print(x); printf(“%d”,x);
printf(“n%d”,x); }
20
10
}
20
10
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10. Pointer and Function
• Do not pass a variable.
print(x);
• Pass address of variable using & operator.
print(&x);
• Allows you to change the value directly at memory
location.
• Arrays are not passed with & because the array name
is already a pointer.
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11. Pointer and Function
• An address can handle by a pointer only.
• Use * operator for variable inside of function.
print(int *x);
• *x is used as an alias for the variable x.
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12. Pointer and Function
• Call by reference
– Pass the address of the variable to the function.
void main() void print(int *y)
{ {
20
10
int x = 10; *y += 10;
print(&x); printf(“%d”,x);
printf(“n%d”,x); }
&x
}
20
20
12

13. Pointer Arithmetic
• ++ or -- : Increment or Decrement
• +, +=,-, -= : Add or subtract an integer from pointer.
• Operations meaningless unless performed on
an array.
int a[5] a a+1 a+2 a+3 a+4
1000 1004 1008 1012 1016
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14. Pointer Arithmetic
• Subtracting pointers
– Returns number of elements.
int x[10], *a, *b;
a = &x[4];
b = &x[2];
printf(“%d”,a-b);
• Pointer comparison ( <, == , > )
– Check which pointer points to the higher numbered
array element.
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15. Pointer and Array
• Array name is a pointer to the first element of
the array.
int a[10];
a 0 1 2 3 4 5 6 7 8 9
• a = &a[0];
• a[0] = *a;
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16. Pointer and Array
0 1 2 3 4 5 6 7 8 9
a a+1a+2a+3a+4a+5a+6a+7 a+8 a+9
• Using + we can access the next element or the
next memory address.
• Use * operator to access the value.
– *(a+2) = a[2]
– a[i] = *(a+i)
16

17. Pass Array to a Function
• Pass name and size of the array to the
function.
• Problem: write a function (printa()) that print
all elements of an array.
• Write a function (scana()) that scan all
elements of an array.
• Put above functions in a file named “astdio.h”
& create main function in other file.
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18. Character Pointer
• A character pointer points to a character
variable.
char *ptr;
ptr = “hello”;
h e l
l o 0
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19. Arrays of Pointers
• Arrays can contain pointers
• For example: an array of strings
char *name[3] = { “rajan”, “sonu”, “hari”};
• name array has a fixed size, but strings can be
of any size.
name[0] • ‘r’ ‘a’ ‘j’ ‘a’ ‘n’ ‘0’
name[1]
• ‘s’ ‘o’ ‘n’ ‘u’ ‘0’
name[2]
• ‘h’ ‘a’ ‘r’ ‘i’ ‘0’
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20. Pointer to Pointers
• A pointer that point to another pointer.
• Use to read:
– Character array.
– Two dimensional array.
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21. Pointer to Pointers
• Declaration
char **reader;
• This can be used to read a character array.
char *name[3] = {“sonu”, “raju”, “hari”};
reader = name;
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22. Two Dimensional Array
• name[5][6];
• name is the address of first element.
• We can say it array of pointers.
• name[0] points to first row.
• name[1] points to second row.
• name[0] is equivalent to name.
• name[1] is equivalent to (name+1).
• ith element can be access by *(name + i).
22

23. Two Dimensional Array
• To access the jth element of ith row.
• name [i][j]
• *(name[i] + j)
• *(*(name + i) + j)
23

24. Mind Bend
• Write a program which performs the following
tasks:
– Initialize an integer array of 10 elements in main().
– Pass the entire array to a function modify().
– In modify() multiply each elements of array by 3.
– Return the control to main() and print the new array
elements in main().
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NEXT IS STRUCTURES
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