Memory Allocation Notes

/* static storage class program example */

#include <stdio.h>

#define MAXNUM 3

void sum_up(void);

int  main()

{

    int count;

    printf("\n*****static storage*****\n");

    printf("Key in 3 numbers to be summed ");

    for(count = 0; count < MAXNUM; count++)

        sum_up();

    printf("\n*****COMPLETED*****\n");

return 0;

}

void sum_up(void)

{

    /* at compile time, sum is initialized to 0 */

    static int sum = 0;

    int num;

    printf("\nEnter a number: ");

    scanf("%d", &num);

    sum += num;

    printf("\nThe current total is: %d\n", sum);

}

/************************Register*********************/

1. ·        Register keyword is used to define local variable.
2. ·        Local variable are stored in register instead of RAM.
3. ·        As variable is stored in register, the Maximum size of variable = Maximum Size of Register
4. ·        unary operator [&] is not associated with it because Value is not stored in RAM instead it is stored in Register.
5. ·        This is generally used for faster access.
6. ·        Common use is “Counter“.
7. 
   

Syntax

{

register int count;

}

Register storage classes example

#include<stdio.h>

void  main()

{

int num1,num2;

register int sum;

printf("\nEnter the Number 1 : ");

scanf("%d",&num1);

printf("\nEnter the Number 2 : ");

scanf("%d",&num2);

sum = num1 + num2;

printf("\nSum of Numbers : %d",sum);

getch();

}

/***********Automatic Storage Classes and Variables**********/

---

This is default storage class

All variables declared are of type Auto by default 

In order to Explicit declaration of variable use ‘auto’ keyword

auto int num1 ;   // Explicit Declaration 

Features :

Storage	Memory
Scope	Local / Block Scope
Life time	Exists as long as Control remains in the block
Default initial Value	Garbage

---

Example :

#include<stdio.h>

#include<conio.h>
void main()
{
 auto mum = 20 ;
 {
      auto num = 60 ;
             printf("nNum : %d",num);
 }
 printf("nNum : %d",num);
}

---

Output :

Num : 60
Num : 20

/**********Malloc*********/

*C program to create memory for int, char and float variable at run time.*/ #include <stdio.h> #include <stdlib.h> int main() {     int *iVar;     char *cVar;     float *fVar;           /*allocating memory dynamically*/           iVar=(int*)malloc(1*sizeof(int));     cVar=(char*)malloc(1*sizeof(char));     fVar=(float*)malloc(1*sizeof(float));           printf("Enter integer value: ");     scanf("%d",iVar);           printf("Enter character value: ");     scanf(" %c",cVar);           printf("Enter float value: ");     scanf("%f",fVar);           printf("Inputted value are: %d, %c, %.2f\n",*iVar,*cVar,*fVar);           /*free allocated memory*/     free(iVar);     free(cVar);     free(fVar);     return 0; }

OUTPUT:-

    Enter integer value: 100

    Enter character value: x

    Enter float value: 123.45

    Inputted value are: 100, x, 123.45