diff --git a/checker.c b/checker.c
new file mode 100644
index 0000000..aa7643a
--- /dev/null
+++ b/checker.c
@@ -0,0 +1,47 @@
+#include <stdio.h>
+#include <ctype.h>
+#define LENGTH 40
+
+int main(void)
+{
+    char ans, correct[LENGTH], input[LENGTH];
+    int i, count, score;
+
+    for (i = 0; i < LENGTH; i++)
+    {
+        ans = ' ';
+        while (!(ans >= 'A' && ans <= 'D'))
+        {
+            printf("%2i : \n", i + 1);
+            scanf(" %c", &ans);
+            ans = toupper(ans);
+        }
+        input[i] = ans;
+    }
+
+    i = 0;
+    ans = ' ';
+    while ((ans = getchar()) != EOF && i < LENGTH)
+        if (ans >= 'A' && ans <= 'D')
+        {
+            correct[i] = ans;
+            i++;
+        }
+
+    score = LENGTH;
+    for (i = 0, count = 0; count < LENGTH / 2; i+= 2, count++)
+            if (input[count] != correct[i])
+            {
+                score--;
+                printf("%i ", count + 1);
+            }
+
+    for (i = 1, count = 20; count < LENGTH; i+= 2, count++)
+            if (input[count] != correct[i])
+            {
+                score--;
+                printf("%i ", count + 1);
+            }
+
+    printf("%i\n", score);
+}