View Compilation Error

0_0_15574709_29965.cpp: In function 'int main()':
0_0_15574709_29965.cpp:5:12: error: initializer-string for array of chars is too long [-fpermissive]
 char w[16]="0123456789ABCDEF";
            ^
0_0_15574709_29965.cpp:18:15: error: 'strlen' was not declared in this scope
     b=strlen(s);
               ^