View Compilation Error

0_0_32766840_8674.cpp:5:11: error: '::main' must return 'int'
 void main(){
           ^
0_0_32766840_8674.cpp: In function 'int main()':
0_0_32766840_8674.cpp:13:16: error: 'strlen' was not declared in this scope
    len=strlen(s);
                ^