Dynamic Memory Allocation In C | Programmerdouts

Dynamic Memory Allocation

• Why Dynamic memory Allocation(DMA)?

• Consider a declaration of array of size 10,int a[10]

• Now as we have declare an array of size 10,so this declaration will reserve 20 bytes for array a in the memory.As array is of int type each element will need 4 bytes so total becomes to 40 Bytes.


• Till now there is no problem with  ordinary way,But what if there was an need of only 5 elements , this makes wastage of memory


• What if , we want to store more than 10 elements.


• Other Reason of Using Dynamic memory Allocation is that we can increase the size at the runtime.


• There are some memory allocations functions with the help of them you can solve above problems.

• Memory Allocating Functions
• malloc()
• calloc()
• realloc()
• free()

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malloc() function

Allocates required size of bytes and returns pointer to the first byte.

let's understand by examples

Syntax : malloc() function

(cast_type *)  malloc(bytes);

If cast type is not specified,than malloc() function returns void pointer.

Let's use malloc() function to allocate memory to integer pointer

#include<stdio.h>
void main()
{
int *p;

p = (int*)malloc(sizeof(int));
 // malloc() function will return integer pointer.


}

sizeof()function gives the bytes acquired by the variable ,data type in the memory

allocating memory to float pointer

#include<stdio.h>
void main()
{
float *p;

p = (float*)malloc(sizeof(float));
 // malloc() function will return float pointer.


}

allocating memory to char pointer

#include<stdio.h>
void main()
{
char *p;

p = (float*)malloc(sizeof(char));
 // malloc() function will return float pointer.


}

Now we will create array by allocating memory dynamically by malloc()

allocating memory for 10 blocks of int type

#include<stdio.h>
void main()
{
int *p;
p = (int*)malloc(sizeof(int)*10);
//it will allocate 40 bytes
//it will return pointer to first byte.

}

Q:create a array of 10 students for storing rollno ,take rollno from the user.Create array dynamically

Solution:

#include<stdio.h>
void main()
{
int i;
int *p;
p = (int*)malloc(sizeof(int)*10);


for(i=0;i < 10;i++)
 {  
    printf("Enter the student roll no:");
    scanf("%d",p+i);
    
 }
}

As p is a pointer which has address of first element , so at every iteration we are adding i value to get address of next block.

At every iteration we are storing value at p+i address which is address of next block

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Q:Create a array of float type of 10 elements ,and store the temperature of past 10 days and print them on the screen.

Solution:

#include<stdio.h>
void main()
{
int i;
float *p;
p = (float*)malloc(sizeof(float)*10);


for(i=0;i < 10;i++)
 {   printf("Enter the Temperature:");
    scanf("%f",p+i);
 }
printf("\ntemperature of past 10 days was: ");
for(i=0;i<10;i++)
 {
    printf("%f\t",*(p+i));
 }
}

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Q:Create an array of int type of 10 elements.take the elements from the user and only print the even number.Create array dynamically.

Solution:

#include<stdio.h>
void main()
{
int i;
int *p;
p = (int*)malloc(sizeof(int)*10);


for(i=0;i < 10;i++)
 {
    printf("\nEnter the Character:");
    scanf("%d",(p+i));

 }
printf("\nEven number are : ");
for(i=0;i < 10;i++)
 {  if(*(p+i) %2 == 0)
    {
     printf("%d\t",*(p+i));
    }
 }
}

This how we can dynamically allocate memory by using malloc() functions.

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