add problem 172 add test function

Author: supercoderhawk

C/151-200/172.-Factorial-Trailing-Zeroes.c

@@ -0,0 +1,21 @@
+/*
+ * Given an integer n, return the number of trailing zeroes in n!.
+ * Note: Your solution should be in logarithmic time complexity.
+ * Created by supercoderhawk on 2017/7/26.
+ */
+#include <stdio.h>
+
+int trailingZeroes(int n) {
+    if (n <= 0)
+        return 0;
+
+    int count = 0;
+    for (long long i = 5; i<=n; i *= 5) {
+        count += n / i;
+    }
+    return count;
+}
+
+void testTrailingZeroes() {
+    printf("%d", trailingZeroes(25));
+}