/in/foo.c: In function 'main':
/in/foo.c:5:13: error: 'i' undeclared (first use in this function)
    5 |         for(i=0;i<20;i++)
      |             ^
/in/foo.c:5:13: note: each undeclared identifier is reported only once for each function it appears in
/in/foo.c:7:26: error: stray '\' in program
    7 |                 sum=sum+a\b;
      |                          ^
/in/foo.c:7:26: error: expected ';' before 'b'
    7 |                 sum=sum+a\b;
      |                          ^~
      |                          ;