function ad(){
         var a=prompt("请输入学号")；
         var b=prompt("请输入姓名");
         
        if (a!=null && b!=null){
             var tr3=document.createElement("tr");
             var td1=document.createElement("td");
             var td2=document.createElement("td");
             var td3=document.createElement("td");
             var a1=document.createElement("a");
             
             td1.innerHTML=a;
             td2.innerHTML=b;
             a1.innerHTML="删除";
             
             var p1=document.getElementById("table")
             p1.appendChild(tr3);
             tr3.appendChild(td1);
             tr3.appendChild(td2);
             tr3.appendChild(td3);
             td3.appendChild(a1);
             
             a1.setAttribute("href","javascript:;");
             a1.setAttribute("onclick","re(this)");
         
     }else{
         ad();
     }