function init(){
	setInputFilter( document.getElementById( "txt_nrc" ), function(value) {
  		return /^\d*\.?\d*$/.test(value);
	} );
}

function agregarDatos(){
	var datos = document.getElementById( "tabladatos" );
	datos.innerHTML += "<tr>"
						+ "<td>" + document.getElementById( "txt_nrc" ).value + "</td>"
						+ "<td>" + document.getElementById( "txt_curso" ).value + "</td>"
						+ "<td>" + document.getElementById( "cmb_horario" ).value + "</td>"
						+ "<td>" + document.getElementById( "chk_estado" ).value + "</td>"
						+ "<td>" + document.querySelector( 'input[ name=rdb_tipo ]:checked' ).value + "</td>"
					+ "</tr>"
}

function setInputFilter(textbox, inputFilter) {
  ["input", "keydown", "keyup", "mousedown", "mouseup", "select", "contextmenu", "drop"].forEach(function(event) {
    textbox.addEventListener(event, function() {
      if (inputFilter(this.value)) {
        this.oldValue = this.value;
        this.oldSelectionStart = this.selectionStart;
        this.oldSelectionEnd = this.selectionEnd;
      } else if (this.hasOwnProperty("oldValue")) {
        this.value = this.oldValue;
        this.setSelectionRange(this.oldSelectionStart, this.oldSelectionEnd);
      } else {
        this.value = "";
      }
    });
  });
}