View Compilation Error

0_0_13492902_14622.cpp: In function 'int main()':
0_0_13492902_14622.cpp:12:23: error: 'strlen' was not declared in this scope
       int len=strlen(a);
                       ^
0_0_13492902_14622.cpp:24:17: error: 'sort' was not declared in this scope
       sort(b,b+j);
                 ^