View Compilation Error

0_0_32754517_15963.cpp: In function 'int main()':
0_0_32754517_15963.cpp:11:3: error: 'len' was not declared in this scope
   len = strlen(str);
   ^
0_0_32754517_15963.cpp:11:19: error: 'strlen' was not declared in this scope
   len = strlen(str);
                   ^