View Compilation Error

0_0_25316969_2894.cpp: In function 'int main()':
0_0_25316969_2894.cpp:12:1: error: 's' was not declared in this scope
 s+=a;}
 ^
0_0_25316969_2894.cpp:13:7: error: 's' was not declared in this scope
 cout<<s<<endl;}
       ^