[C Language] Data Structure-preparation knowledge dynamic memory allocation, data structure dynamic memory

[C Language] Data Structure-preparation knowledge dynamic memory allocation, data structure dynamic memory

Dynamic Memory Allocation

Static Memory Allocation array int a [5] = {1, 2, 3, 4, 5}

Dynamic Memory Allocation Array

Int len = 5;

Int * parr = (int *) malloc (sizeof (int) * len );

1. 4*5 = 20 bytes of memory is allocated, and the address of the first byte is returned.

2. The address of the first byte is meaningless, so it is forcibly converted to an int type address int *

3. parr points to the address of the first byte, which is equivalent to.

* Parr = 4 <=> a [0] = 4

Parr [1] <==> a [1]

4. release memory

Free (parr) releases the dynamically allocated 20 bytes of memory represented by parr.

 

#include <stdio.h>
#include <malloc.h>
int main (void) {

         printf ("% s \ n", "Please enter the length of the array");
         int len;
         scanf ("% d", & len);
         // Dynamic allocation of memory
         int * parr = (int *) malloc (sizeof (int) * len);
         int i;
         for (i = 0; i <len; i ++) {
                 printf ("Element:");
                 scanf ("% d", & parr [i]); // Another way, * (parr + i)
         }
         for (i = 0; i <len; i ++) {
                 printf ("% d \ n", parr [i]); // Used as an ordinary array
         }
         // Free up memory
         free (parr);
}