Int stack (push/pop/peek)

Challenge

Given the supplied struct

typedef struct { int *data; size_t cap, len; } istack_t;

implement:

• void stack_init(istack_t *s)
• void stack_free(istack_t *s)
• int stack_push(istack_t *s, int v) — grow if needed, return 0 on success
• int stack_pop(istack_t *s, int *out) — return 0 on success, -1 on empty
• int stack_peek(const istack_t *s, int *out) — return 0 on success, -1 on empty

All allocations use malloc/realloc/free.

Starter code

#include <stdlib.h>
#include <stddef.h>

void stack_init(istack_t *s){ /* TODO */ }
void stack_free(istack_t *s){ /* TODO */ }
int  stack_push(istack_t *s, int v){ /* TODO */ return -1; }
int  stack_pop (istack_t *s, int *out){ /* TODO */ return -1; }
int  stack_peek(const istack_t *s, int *out){ /* TODO */ return -1; }