foo.cc: In function 'int main()':
foo.cc:10:9: error: 'len2' was not declared in this scope; did you mean 'lenb'?
   10 |         len2=sb.size();
      |         ^~~~
      |         lenb
foo.cc:17:19: error: 'lena' was not declared in this scope; did you mean 'lenb'?
   17 |         for(i=0;i<lena;i++){
      |                   ^~~~
      |                   lenb
foo.cc:22:19: error: 'lena' was not declared in this scope; did you mean 'lenb'?
   22 |         for(i=0;i<lena+lenb;i++){
      |                   ^~~~
      |                   lenb
foo.cc:28:17: error: 'lena' was not declared in this scope; did you mean 'len'?
   28 |         int len=lena+lenb-1;
      |                 ^~~~
      |                 len

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