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

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

@@ -0,0 +1,49 @@
+#include <ctype.h>
+#include <stdbool.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include "input.h"
+#include "stack.h"
+
+bool is_integer(char* string) {
+  size_t string_length = strlen(string);
+  for (size_t index = 0; index < string_length; index++) {
+    if (!isdigit(string[index])) {
+      return false;
+    }
+  }
+  return true;
+}
+
+int main() {
+  char* string = input();
+  struct Stack* stack = stack_initialization();
+  char* token = strtok(string, " ");
+  while (token != NULL) {
+    if (is_integer(token)) {
+      intptr_t number;
+      sscanf(token, "%ld", &number);
+      stack_push(stack, (void*)number);
+    } else {
+      intptr_t number1 = (intptr_t)stack_pop(stack);
+      intptr_t number2 = (intptr_t)stack_pop(stack);
+      intptr_t result = 0;
+      if (strcmp(token, "+") == 0) {
+        result = number2 + number1;
+      } else if (strcmp(token, "-") == 0) {
+        result = number2 - number1;
+      } else if (strcmp(token, "*") == 0) {
+        result = number2 * number1;
+      } else {
+        result = number2 / number1;
+      }
+      stack_push(stack, (void*)result);
+    }
+    token = strtok(NULL, " ");
+  }
+  printf("%ld\n", (intptr_t)stack_pop(stack));
+  return EXIT_SUCCESS;
+}