View Compilation Error

0_0_30476601_4344.cpp: In function 'int main(int, const char**)':
0_0_30476601_4344.cpp:16:31: error: 'strlen' was not declared in this scope
   for (i = 0, len = strlen(str); i < len; i++)
                               ^
0_0_30476601_4344.cpp:25:31: error: 'strlen' was not declared in this scope
   for (i = 0, len = strlen(str); i < len; i++)
                               ^