/in/foo.c: In function 'main':
/in/foo.c:16:5: error: 'else' without a previous 'if'
   16 |     else if(d==0)
      |     ^~~~
/in/foo.c:20:9: error: 'else' without a previous 'if'
   20 |         else{e=-b/2/a;f=sqrt(-d)/2/a;
      |         ^~~~