add function stack_push

just like the tittle. Thanks for the review. ;D

stack.c

-#include "stack.h"
-#include <stdio.h>
 #include <stdlib.h>
+#include "stack.h"
+
 
 #define DEFAULT_CAPACITY 4
 
@@ -17,6 +17,18 @@ void stack_destroy(stack *s) {
     s->top      = -1;
 }
 
+void stack_push(stack *s, int value)
+{
+    if (s->top == s->capacity-1)
+    {
+        assert(s->data = realloc(s->capacity * 2 * sizeof(int)));
+        s->capacity=s->capacity * 2;
+    }
+
+    s->top++;
+    s->data[s->top] = value;
+}
+
 void stack_pop(stack *s, int *value) {
     if (stack_is_empty(*s)) {
         return;
@@ -62,3 +74,4 @@ void stack_clone(stack s, stack *clone) {
 int get_length(stack s) {
     return s.top + 1;
 }
+