View Compilation Error

0_0_20075537_19683.cpp:6:11: error: '::main' must return 'int'
 void main(){
           ^
0_0_20075537_19683.cpp: In function 'int main()':
0_0_20075537_19683.cpp:11:27: error: 'strlen' was not declared in this scope
   int len_a = strlen(str_a) ;
                           ^
0_0_20075537_19683.cpp:16:25: error: 'strcmp' was not declared in this scope
    if(strcmp(str_a,str_b))
                         ^