diff --git a/day5/d3.cpp b/day5/d3.cpp
new file mode 100644
index 0000000..899afaf
--- /dev/null
+++ b/day5/d3.cpp
@@ -0,0 +1,12 @@
+// 进制转换
+#include <iostream>
+
+using namespace std;
+
+int main()
+{
+    int n1 = 037, n2 = 0x3a;
+    cout << "037 = " << n1 << endl;  // 以10进制输出八进制数
+    cout << "0x3a = " << n2 << endl; // 以10进制输出十六进制数
+    return 0;
+}
\ No newline at end of file