View Compilation Error

0_0_31513095_1500.cpp: In function 'int main()':
0_0_31513095_1500.cpp:13:3: error: 'n' was not declared in this scope
   n=strlen(b);
   ^
0_0_31513095_1500.cpp:14:3: error: 'm' was not declared in this scope
   m=strlen(a);
   ^