added function

src/primzahl/main.c

@@ -8,5 +8,10 @@ int main() {
 
     int num = usergetd("Enter a positive number: ", minInput, NULL);
 
+    if (primzahl(num))
+        printf("%d is a prime number.\n", num);
+    else
+        printf("%d is not a prime number.\n", num);
+
     return 0;
 }