C Dynamic Arrays with realloc

When you do not know the size in advance, allocate with malloc and grow with realloc. Always check the result and free the memory.

ExampleC

#include <stdio.h>
#include <stdlib.h>

int main(void) {
  int capacity = 2;
  int count = 0;
  int *data = malloc(capacity * sizeof(int));
  if (data == NULL) return 1;

  for (int i = 1; i <= 7; i++) {
    if (count == capacity) {
      capacity *= 2;
      int *bigger = realloc(data, capacity * sizeof(int));
      if (bigger == NULL) { free(data); return 1; }
      data = bigger;
      printf("grew to %d\n", capacity);
    }
    data[count++] = i * i;
  }

  for (int i = 0; i < count; i++) printf("%d ", data[i]);
  printf("\n");
  free(data);
  return 0;
}

Output

grew to 4
grew to 8
1 4 9 16 25 36 49

Quick check

What must you always do with memory from malloc?

free it when doneSet it to zeroDeclare it const

Finish the quick check (and any code exercise) to complete this lesson, or mark it done yourself.

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