foo.c: In function ‘main’:
foo.c:5:23: error: expected ‘;’ before ‘)’ token
    5 |         for (i = 1;i++);
      |                       ^
      |                       ;
foo.c:5:9: warning: this ‘for’ clause does not guard... [-Wmisleading-indentation]
    5 |         for (i = 1;i++);
      |         ^~~
foo.c:6:9: note: ...this statement, but the latter is misleadingly indented as if it were guarded by the ‘for’
    6 |         {
      |         ^
foo.c:4:17: warning: unused variable ‘sum’ [-Wunused-variable]
    4 |         int i,j,sum=0;
      |                 ^~~