View Compilation Error

0_0_24252706_24510.cpp: In function 'int main()':
0_0_24252706_24510.cpp:18:9: error: 'len' was not declared in this scope
         len=strlen(s);
         ^
0_0_24252706_24510.cpp:18:21: error: 'strlen' was not declared in this scope
         len=strlen(s);
                     ^