表示函数
\(y\)\(=\)
\(f\)\(( \)
\(x\)\()\)的程序如图所示
\(INPUT x\)
\(IF x > 0 THEN\)
\(y=1\)
\(ELSE\)
\(IF x=0 THEN\)
\(y=0\)
\(ELSE\)
\(y=-1\)
\(END IF\)
\(END IF\)
\(PRINT y\)
\(END\)
则关于函数\(y\)\(=\)\(f\)\((\)\(x\)\()\)有下列结论：
\(①\)\(y\)\(=\)\(f\)\((\)\(x\)\()\)的图象关于原点对称．
\(②\)\(y\)\(=\)\(f\)\((\)\(x\)\()\)的值域为\([-1,1]\)．
\(③\)\(y\)\(=\)\(f\)\((\)\(x\)\()\)是周期\(T\)\(=1\)的周期函数．
\(④\)\(y\)\(=\)\(f\)\((\)\(x\)\()\)在\(R\)上是增函数．
\(⑤\)函数\(y\)\(=\)\(f\)\((\)\(x\)\()-\)\(kx\)\((\)\(k\)\( > 0)\)有三个零点．
则正确结论的序号为________\(.(\)填上所有正确结论的序号\()\)