View Compilation Error

0_0_29623198_4245.cpp: In function 'int main()':
0_0_29623198_4245.cpp:13:3: error: 'lena' was not declared in this scope
   lena=strlen(a);
   ^
0_0_29623198_4245.cpp:14:3: error: 'lenb' was not declared in this scope
   lenb=strlen(b);
   ^