foo.cc: In function 'int main()':
foo.cc:7:9: warning: variable 'len1' set but not used [-Wunused-but-set-variable]
     int len1,len2;
         ^~~~
foo.cc:10:10: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
     scanf("%s",str2);
     ~~~~~^~~~~~~~~~~

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