View Compilation Error

0_0_36112777_19501.cpp:5:11: error: '::main' must return 'int'
 void main(){
           ^
0_0_36112777_19501.cpp: In function 'int main()':
0_0_36112777_19501.cpp:13:31: error: 'strlen' was not declared in this scope
         for(int i=0;i<strlen(s);++i){
                               ^