function sum(){
    var items = document.getElementsByName("cost");
   var suma=0;
    var sumap=0;
    for(var i=0;items.length;i++){
        suma+=parseFloat(items[i].innerHTML);
    }
    sumap=suma/items.length;
    var avg = document.getElementById('average').innerText ='Students(average grade: '+suma+')';

}

function getParams(){
    var name = document.getElementById("name");
    var index = document.getElementById("index");
    var phone = document.getElementById("phone");
    var ocenki=document.getElementsByName("grade");
    for(var i=0;i<ocenki.length;i++){
        if(ocenki[i].checked){
            var grade=ocenki[i].value;
        }
    }
    var sesija=document.getElementById("session");
    if(name.value=="" || index.value=="" || phone.value=="" || grade.value=="" || sesija.value ==""){
        alert("Site polinja mora da se popolnat");
    }else
        var row=document.createElement("tr");
        var cell1=document.createElement("td");
        var cell2=document.createElement("td");
    var cell3=document.createElement("td");
    var cell4=document.createElement("td");
    cell4.setAttribute('name','cost');
    var cell5=document.createElement("td");
    var cell6=document.createElement("td");
    var button1=document.createElement("button");
    var text=document.createTextNode("Confirm");
    button1.setAttribute('onclick','colorRow(this)');
    button1.appendChild(text);
    var button2=document.createElement("button");
    var text2=document.createTextNode("Remove");
    button2.setAttribute('onclick','removeRow(this)');
    button2.appendChild(text2);
    var cellText1 = document.createTextNode(name.value);
    var cellText2 = document.createTextNode(index.value);
    var cellText3 = document.createTextNode(phone.value);
    var cellText4 = document.createTextNode(grade);
    var cellText5 = document.createTextNode(sesija.value);
    var tabela = document.getElementById("tabela");
    cell1.appendChild(cellText1);
    cell2.appendChild(cellText2);
    cell3.appendChild(cellText3);
    cell4.appendChild(cellText4);
    cell5.appendChild(cellText5);
    cell6.appendChild(button1);
    cell6.appendChild(button2);
    row.appendChild(cell1);
    row.appendChild(cell2);
    row.appendChild(cell3);
    row.appendChild(cell4);
    row.appendChild(cell5);
    row.appendChild(cell6);
    tabela.appendChild(row);
    sum();

}
function colorRow(row) {
    var tr = row.parentNode;
    tr.parentNode.style.backgroundColor = 'lightgreen';
    row.setAttribute('disabled','true');
    row.parentNode.lastElementChild.setAttribute('disabled','true');
}
function removeRow(ref){
    var tr=ref.parentNode.parentNode;
    tr.parentNode.removeChild(tr);
    var index=document.getElementById('index');
    var ocenki=document.getElementsByName('grade');
    for(var i=0;i<ocenki.length;i++){
        if(ocenki[i].checked){
            var grade=ocenki[i].value;
        }
    }
    var lista = document.getElementById('history');
    var li=document.createElement('li');
    var text=document.createTextNode(index.value + '- grade' + grade);
    li.appendChild(text);
    lista.appendChild(li);
    sum();
}