View Compilation Error

0_0_18941291_25488.cpp: In function 'int main()':
0_0_18941291_25488.cpp:20:8: error: 'len1' was not declared in this scope
     w1[len1] = ch1[i];
        ^
0_0_18941291_25488.cpp:30:8: error: 'len2' was not declared in this scope
     w2[len2] = ch2[i];
        ^