View Compilation Error

0_0_23080854_25330.cpp: In function 'int main()':
0_0_23080854_25330.cpp:6:25: error: 'a' was not declared in this scope
     while(scanf("%s %s",a,b)!=EOF)
                         ^
0_0_23080854_25330.cpp:6:27: error: 'b' was not declared in this scope
     while(scanf("%s %s",a,b)!=EOF)
                           ^