feat(solutions): add reverse-polish-notation/c/function

challenges/reverse-polish-notation/solutions/c/function/stack.c

@@ -0,0 +1,40 @@
+#include "stack.h"
+
+#include <stdio.h>
+#include <stdlib.h>
+
+struct Stack *stack_initialization() {
+  struct Stack *stack = malloc(sizeof(*stack));
+  if (stack == NULL) {
+    exit(EXIT_FAILURE);
+  }
+  stack->first = NULL;
+  stack->length = 0;
+  return stack;
+}
+
+void stack_push(struct Stack *stack, void *data) {
+  struct Node *node_new = malloc(sizeof(*node_new));
+  if (stack == NULL || data == NULL) {
+    exit(EXIT_FAILURE);
+  }
+  node_new->data = data;
+  node_new->next = stack->first;
+  stack->first = node_new;
+  stack->length = stack->length + 1;
+}
+
+void *stack_pop(struct Stack *stack) {
+  if (stack == NULL) {
+    exit(EXIT_FAILURE);
+  }
+  struct Node *node = stack->first;
+  void *data = NULL;
+  if (node != NULL) {
+    stack->first = node->next;
+    data = node->data;
+    free(node);
+  }
+  stack->length = stack->length - 1;
+  return data;
+}