使用while 循环输出100-50，从大到小，如100，99，98…，到50时再从0循环输出到50，然后结束。

n = 100
while n>=50:
    print(n)
    n -= 1
m = 0
while m<=50:
    print(m)
    m += 1

# 一行打印
s = ''
s1 = ","
n = 100
while n >= 50:
    s += str(n) + s1
    n -= 1
m = 0
while m <= 50:
    if m == 50:
        s += str(m)
    else:
        s += str(m) + s1
    m += 1
print(s)