foo.cc: In function 'int main()':
foo.cc:20:19: error: 'len1' was not declared in this scope; did you mean 'lena'?
   20 |         a[i] = s1[len1-i-1] - '0';
      |                   ^~~~
      |                   lena
foo.cc:25:19: error: 'len2' was not declared in this scope; did you mean 'lenb'?
   25 |         b[i] = s2[len2-i-1] - '0';
      |                   ^~~~
      |                   lenb

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