This document discusses stacks and heaps in computer memory. It defines a stack as a linear data structure where items are inserted and deleted from one end in LIFO order. Compiler stores local variables in the stack. Writing to the stack is called push and deleting is called pop. The heap is an area of dynamic memory allocation where space is allocated during program execution using functions like malloc(), calloc(), and realloc(). The stack has limits and fixed-size variables while the heap allows variable resizing and globally accessible variables of arbitrary size.

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Stack and Heap

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4. Stack
• Stack is a linear data structure in which a data item is
inserted and deleted at one record.
• A stack is called LIFO(Last In First Out) or
FILO(First In Last Out) structure.
• The first item added to a stack is the last item
removed from a stack.
• Compiler store the local variable inside the stack.

5. Push and Pop
• Writing a value to the stack is called push.
• Deleting a value from stack is called pop.

6. #include <stdio.h>
int hcf(int n1, int n2);
int main()
{
int n1, n2;
n1=24;
n2=16;
printf("H.C.F of %d and %d = %d", n1, n2, hcf(n1,n2));
return 0;
}
int hcf(int n1, int n2)
{
i f(n2!=0)
return hcf(n2, n1%n2);
else
return n1;
}

7. 1.main()
n1=24
n2=16
2.hcf(24,16)
3.hcf(16,24%16)=hcf(16,8)
4.hcf(8,16%8)=hcf(8,0)n1=24
n2=16
hcf(24,16)
hcf(16,8)
hcf(8,0)
STACK
Representation of stack operation

8. Heap
• The heap is an area of memory reserved for dynamic
memory allocation.
• Dynamic allocation is a technique in which a program
can acquire storage space in main memory.
• In this method , the space for the program is allocated
from the free space during execution of the program.
• This free space is called Heap

9. Memory allocation functions
1. malloc()
This function is used to allocate memory space in
bytes to the variable of different data types.
Example: ptr = (int*)malloc(20);
Ptr=(data type*)malloc(given size);

10. #include<stdio.h>
#include<stdlib.h>
main()
{
int k,*p,j=0,sum=0;
printf("How many numbers:");
scanf("%d",&k);
p=(int*)malloc(k*sizeof(int));
printf("n enter the numbers");
while(j!=k)
{
scanf("%d", p+j);
j++;
}
j=0;
printf("sum: ");
while(j!=k)
{
sum=sum+*(p+j);
j++;
}
printf("%d",sum);
}
How many numbers:3
enter the numbers: 1 2 3
Sum: 6

11. 2. calloc()
• This function is useful for allocating multiple blocks
of memory . It is declared with two arguments.
• It allocate 4 blocks of memory and each block
contain 2 bytes
• This function is usually used for allocating memory
for array and structure
Ptr =(int*)calloc(4,2);

12. #include<stdio.h>
#include<stdlib.h>
main()
{
int k,*p,j=0,sum=0;
printf("How many numbers:");
scanf("%d",&k);
p=(int*)calloc(k,2);
printf("nenter the numbers");
while(j!=k)
{
scanf("%d",p+j);
j++;
}
j=0;
printf("sum: ");
while(j!=k)
{
sum=sum+*(p+j);
j++;
}
printf("%d",sum);
}
How many numbers:3
enter the numbers: 1 2 3
Sum: 6

13. 3.free()
• This function is used to release the memory allocated
by memory allocating functions.
• ptr is the pointer and free() releases the memory
occupied by the pointer variable.
free(ptr);

14. 4.realloc()
• This function reallocate the main memory.
• This are made to shrink or enlarge the previously
allocated memory.
• It returns the address of the reallocated block.
• If the block cannot be reallocated returns NULL

15. #include<stdio.h>
#include<stdlib.h>
main()
{
char *str;
str=(char*)malloc(6);
str=("india");
printf("str=%s",str);
str=(char*)realloc(str,10);
str=("hindustan");
printf("nnew str=%s",str);
free(str);
}
str=india
new str=hindustan

16. Stack vs Heap
stack
• local variables only.
• limit on stack size.
• variables cannot be resized.
• space is managed efficiently
by CPU, memory will not
become fragmented .
heap
• variables can be accessed
globally .
• no limit on memory size.
• variables can be resized
using realloc() .
• no guarantee on efficient use
of space.

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