foo.c:2:1: warning: return type defaults to 'int' [-Wimplicit-int]
 main()
 ^~~~
foo.c: In function 'main':
foo.c:4:5: error: 'n' undeclared (first use in this function)
  if(n>=0,0<=m<=30);
     ^
foo.c:4:5: note: each undeclared identifier is reported only once for each function it appears in
foo.c:4:13: error: 'm' undeclared (first use in this function)
  if(n>=0,0<=m<=30);
             ^
foo.c:4:9: warning: left-hand operand of comma expression has no effect [-Wunused-value]
  if(n>=0,0<=m<=30);
         ^
foo.c:5:6: warning: unused variable 'n' [-Wunused-variable]
  int n;
      ^

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