Initial version w/o timing or counters.

.gitignore

+cube-test
+.*.swp

Makefile

+#
+# Makefile
+# Kevin Lyda, 2017-10-12 19:14
+#
+
+cube-test: cube-test.c
+	cc -Wall -o cube-test cube-test.c
+
+
+# vim:ft=make
+#

cube-test.c

+/*
+ * cube-test.c
+ * Copyright (C) 2017 Kevin Lyda <kevin@phrye.com>
+ *
+ * Distributed under terms of the GPL license.
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <time.h>
+
+int
+random_two_digit_number() {
+  return (rand() % 90) + 10;
+}
+
+int
+cube(int n) {
+  return n * n * n;
+}
+
+int
+read_number() {
+  char buf[10];
+
+  if (!fgets(buf, sizeof buf, stdin)) {
+    return 0;
+  }
+  return atoi(buf);
+}
+
+int
+main(int argc, char *argv[]) {
+  int guess, number;
+
+  srand(time(NULL));
+
+  while (1) {
+    number = random_two_digit_number();
+    printf("Number is %d. Cube root (0 to exit)? ", cube(number));
+    guess = read_number();
+    if (guess == 0) {
+      exit(0);
+    }
+    if (guess == number) {
+      printf("Correct.\n");
+    } else {
+      printf("Not correct. Number was %d.\n", number);
+    }
+  }
+}