function addQtd(idelemento) {
    var formulario = document.getElementsByName(idelemento)[0];
    if (!isNaN(formulario.value) || formulario.value == "") {
        formulario.value = parseInt(formulario.value) + 1;
    }
}

function remQtd(idelemento) {
    var formulario = document.getElementsByName(idelemento)[0];
    if (!isNaN(formulario.value) || formulario.value == "") {
        if (formulario.value >= 2) {
            formulario.value = parseInt(formulario.value) - 1;
        }
    }
}