方法一:
let y = Number(prompt('请输入年份'));
let m = Number(prompt('请输入月份'));
let d = Number(prompt('请输入几日'));
let sum = 0;
switch (m) {
case 12:
sum += 30;
case 11:
sum += 31;
case 10:
sum += 30;
case 9:
sum += 31;
case 8:
sum += 31;
case 7:
sum += 30;
case 6:
sum += 31;
case 5:
sum += 30;
case 4:
sum += 31;
case 3:
if (y % 4 == 0 && y % 100 != 0 || y % 400 == 0) {
sum += 29;
} else {
sum += 28;
}
case 2:
sum+=31;
case 1:
sum+=d;
}
alert('这是'+y+'年的第'+sum+'天');
方法二、
let y = Number(prompt('请输入年份'));
let m = Number(prompt('请输入月份'));
let d = Number(prompt('请输入几日'));
let sum = 0;
let i = 0;
while (i < m) {
switch (i) {
case 1:
case 3:
case 5:
case 7:
case 8:
case 10:
case 12:
sum += 31
break;
case 2:
if (y % 4 == 0 && y % 100 != 0 || y % 400 == 0) {
sum += 29
} else {
sum += 28
}
break;
case 4:
case 6:
case 9:
case 11:
sum += 30
break;
}
i++;
}
alert('这是'+y+'年的第'+sum+'天');