题解 | #【模板】栈#

var stack = [];
while(n--) {
    var strArr = readline().split(' ');
    switch (strArr[0]) {
        case 'push': 
            stack.push(parseInt(strArr[1]));
            break;
        case 'pop':
            if(stack.length == 0) console.log('error');
            else {
                console.log(stack.pop());
            } 
            break;
        case 'top':
            if(stack.length == 0) console.log('error');
            else console.log(stack[stack.length-1]);
            break;
    }   
}