foo.c: In function 'main':
foo.c:4:12: error: 'y' undeclared (first use in this function)
    4 |      int x=y,a,b,c,d;
      |            ^
foo.c:4:12: note: each undeclared identifier is reported only once for each function it appears in
foo.c:5:12: warning: comparisons like 'X<=Y<=Z' do not have their mathematical meaning [-Wparentheses]
    5 |      if(a*3<=x<a*3+3)c=a;
      |         ~~~^~~
foo.c:7:6: error: 'sum' undeclared (first use in this function)
    7 |      sum=0
      |      ^~~
foo.c:7:11: error: expected ';' before 'for'
    7 |      sum=0
      |           ^
      |           ;
    8 |      for(c+d>=3)
      |      ~~~   
foo.c:10:13: warning: statement with no effect [-Wunused-value]
   10 |      for(c+d<3)
      |          ~~~^~
foo.c:10:15: error: expected ';' before ')' token
   10 |      for(c+d<3)
      |               ^
      |               ;
foo.c:10:15: error: expected expression before ')' token

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