View Compilation Error

0_0_38586817_617.cpp: In function 'int main()':
0_0_38586817_617.cpp:13:6: error: 'strlen' was not declared in this scope
    a=strlen(arr)-1;
      ^~~~~~
0_0_38586817_617.cpp:13:6: note: 'strlen' is defined in header '<cstring>'; did you forget to '#include <cstring>'?
0_0_38586817_617.cpp:2:1:
+#include <cstring>
 
0_0_38586817_617.cpp:13:6:
    a=strlen(arr)-1;
      ^~~~~~