View Compilation Error

0_0_35952664_3320.cpp:3:11: error: '::main' must return 'int'
 void main()
           ^
0_0_35952664_3320.cpp: In function 'int main()':
0_0_35952664_3320.cpp:9:15: error: 'strlen' was not declared in this scope
   len=strlen(a);
               ^