foo.c: In function 'main':
foo.c:6:9: error: 'y1' undeclared (first use in this function); did you mean 'x1'?
    6 |         y1=x1+x2;
      |         ^~
      |         x1
foo.c:6:9: note: each undeclared identifier is reported only once for each function it appears in
foo.c:7:9: error: 'y2' undeclared (first use in this function); did you mean 'x2'?
    7 |         y2=x1*x2;
      |         ^~
      |         x2
foo.c:8:9: error: 'y3' undeclared (first use in this function)
    8 |         y3=x1%x2;
      |         ^~
foo.c:9:40: error: expected ';' before 'return'
    9 |         printf("%d","%d","%d",y1,y2,y3)
      |                                        ^
      |                                        ;
   10 |                 return 0
      |                 ~~~~~~                  

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