POINTERS IN C - BTECH BCA CS AND IT PRESENTATIONS

1. Pointer
Arithmetic
Paurush Sinha

2. Analogy: Incrementing and Decrementing Pointer
What if, we use increment or decrement operator in pointers, like we do with
integer data type.
Analogy with Integer
#include <stdio.h>
int main(){
int a = 1;
int b;
b = a++;
printf("a: %d b: %d", a, b);
return 0;
}
Output
a: 2 b: 1​

3. Implementation:
Incrementing and
Decrementing
Pointer
So if we follow similar syntax as followed
in last slide for integers, as shown in code
below.
#include <stdio.h>
int main(){
int *a = 1;
a*++;
printf("%d", *a);
return 0;
}
So, will it increment the value of integer stored in
the address of the pointer? Not really.

4. Theory: Incrementing and Decrementing Pointer
If you use increment or decrement operator on pointer, C will
increment or decrement pointer to respective memory address.
Hence, the code in previous slide will not increment the value,
instead will increment the pointer address.
Address 100 200 300
Value 1 2 3

5. Sounds Great?

6. Example of
Increment and
Decrement in
Pointers
Let's dive into the syntactically correct and
working example of the Pointer Arithmetic.
Code
#include <stdio.h>
int main(){
int a = 1;
int *b = &a;
printf("Value: %dn", *b);
*b++;
printf("Value: %d", *b);
return 0;
}
Output​
Value: 1​
Value: 1662454488

7. But, Why a random number?
After incrementing we can notice a random number because,
after incrementation, pointer has changed the address to
another memory location, so, the new target location may
already have a value stored by any other program running on
the computer, or may have some garbage value.
Address 100 200 300
Value 1454545 1 54654646

8. Using pointers to
iterate through arrays

9. Using pointers to iterate through arrays
Now, we know that increment and decrement operators,
increment to next pointer address and decrement to previous
pointer address respectively. Using this analogy we can
implement it in array. So, in array, we can use increment
operator on pointer to jump to next index of the array and
decrement operator to jump to previous index in array.

10. Aim
Let's say we have an array as
below.
int a[2] = {1,2,3};
We have to print all elements of
array using pointers.

11. Implementation
We can use the code below.
#include <stdio.h>
int main(){
int a[2] = {1,2,3};
int *b = &a[0];
for (int i=1;i<10;i++){
printf("%d. %dn", i, *b);
*b++;
}
return 0;
}
So we are running loop for 9 iterations, to show
you with some garbage values.

12. Output 1. 1
2. 2
3. 3
4. 927276744
5. 32765
6. 4198800
7. 0
8. -1679463158
9. 32626

13. Pointer and Function

14. How to pass
address to
function
You can pass address of a variable using address
operator. And get the value by creating pointer in
parameters in function.
Refer to the code below
#include <stdio.h>
void dothis(int *a){
printf("%d", *a);
}
int main(){
int b = 1;
dothis(&b);
return 0;
}