foo.c: In function 'main':
foo.c:13:13: error: 'n' undeclared (first use in this function)
   13 |         y=a*n;
      |             ^
foo.c:13:13: note: each undeclared identifier is reported only once for each function it appears in
foo.c:21:27: error: 'm' undeclared (first use in this function)
   21 |         printf("%d\t%d",b,m/b);
      |                           ^
foo.c:5:21: warning: variable 'y' set but not used [-Wunused-but-set-variable]
    5 |         int a,b,c,x,y;
      |                     ^

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