foo.c: In function 'main':
foo.c:20:3: warning: this 'if' clause does not guard... [-Wmisleading-indentation]
   if(s(a)==0);
   ^~
foo.c:21:4: note: ...this statement, but the latter is misleadingly indented as if it were guarded by the 'if'
    i=0;
    ^
foo.c:24:7: warning: suggest parentheses around assignment used as truth value [-Wparentheses]
    if(i=0)
       ^
foo.c: In function 's':
foo.c:13:1: warning: control reaches end of non-void function [-Wreturn-type]
 }
 ^
foo.c: In function 'main':
foo.c:17:2: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d",&a);
  ^~~~~~~~~~~~~~

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