View Compilation Error

0_0_1808034_17854.cpp: In function `int main()':
0_0_1808034_17854.cpp:51: error: `len1' undeclared (first use this function)
0_0_1808034_17854.cpp:51: error: (Each undeclared identifier is reported only once for each function it appears in.)
0_0_1808034_17854.cpp:51: error: `len2' undeclared (first use this function)