View Compilation Error

0_0_36041748_16600.cpp: In function 'int main()':
0_0_36041748_16600.cpp:6:18: error: 's1' was not declared in this scope
  while(cin>>hex>>s1>>hex>>s2) 
                  ^
0_0_36041748_16600.cpp:6:27: error: 's2' was not declared in this scope
  while(cin>>hex>>s1>>hex>>s2) 
                           ^