/in/foo.c: In function 'main':
/in/foo.c:6:9: warning: spurious trailing '%' in format [-Wformat=]
  scanf("%",&a,&b);
         ^
/in/foo.c:6:8: warning: too many arguments for format [-Wformat-extra-args]
  scanf("%",&a,&b);
        ^~~
/in/foo.c:7:8: warning: 'Pl' is used uninitialized in this function [-Wuninitialized]
  S=(Pl)*a*a;
    ~~~~^~