foo.cc: In function ‘int main()’:
foo.cc:9:51: error: expected ‘;’ before ‘if’
    9 |         b=a%10*1000+a/10%10*100+a/100%10*10+a/1000
      |                                                   ^
      |                                                   ;
   10 |         if(a<b)
      |         ~~                                         
foo.cc:12:9: error: ‘else’ without a previous ‘if’
   12 |         else
      |         ^~~~