add function stack_push

README.md

 # stack
+# ohayo onii chan !
 

stack.c

+#include "stack.h"
+
+void stack_push(stack *s, int val)
+{
+    if (s->top == s->capacity-1)
+    {
+        assert(s->data = realloc(s->capacity * 2 * sizeof(int)) && "Error : realloc failed");
+    }
+    
+    s->top++;
+    s->data[s->top] = val;
+}
\ No newline at end of file

stack.h

 #ifndef _STACK_H_
 #define _STACK_H_
 
+
 typedef struct _stack {
     int *data;
     int capacity;
     int top;
 } stack;
+void stack_push(stack *s, int val);
 
 #endif