View Compilation Error

0_0_29210830_11549.cpp: In function 'int main()':
0_0_29210830_11549.cpp:10:65: error: 'len' was not declared in this scope
 for (int i=0; i<lena; i++)na[lena-1-i]=a[i]-'0';for (int j=0; j<len
                                                                 ^
0_0_29210830_11549.cpp:10:65: error: expected ';' at end of input
0_0_29210830_11549.cpp:10:65: error: expected primary-expression at end of input
0_0_29210830_11549.cpp:10:65: error: expected ')' at end of input
0_0_29210830_11549.cpp:10:65: error: expected statement at end of input
0_0_29210830_11549.cpp:10:65: error: expected '}' at end of input
0_0_29210830_11549.cpp:10:65: error: expected '}' at end of input