Summary - Memory and stack

Combine malloc, free and realloc to write a dynamic array.

Summary - Memory and stack

In this group you learned C's memory model. Local variables live on the stack; what you allocate with malloc lives on the heap. Automatic storage needs no free; the heap is yours to manage.

int a = 10;                 /* stack */
int *p = malloc(sizeof(int)); /* heap */
int *z = calloc(3, sizeof(int));
free(p); free(z);            /* release */

Every malloc/calloc must have a free; otherwise memory leaks. With realloc you can grow or shrink memory. Now you will do an exercise that combines these concepts.

Exercise malloc, use, free: square computation

Allocate an int with malloc; assign *p = 7. Compute its square with (*p) * (*p); print it with printf. Release the memory with free. Include the <stdlib.h> header.

Show example solution

#include <stdlib.h>
int *p = malloc(sizeof(int));
*p = 7;
int sq = (*p) * (*p);
printf("%d\n", sq);
free(p);

Test yourself

Match function to task

malloc

Allocates on heap
calloc

Allocates zeroed
realloc

Resizes
free

Releases
Which memory must be released with free?
- Local variable
- Memory allocated with malloc
- Static variable
- Array element
Show answer

Memory allocated with malloc — Heap memory allocated with malloc/calloc is released with free.

Fill in the blank: malloc + sizeof

int *p = ____(sizeof(int));

Show answer

int *p = malloc(sizeof(int));

Next lesson: #define

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