while(1):
n=int(input("請輸入非負整數n:"))
if(n>=0):break
if(int(n)==0):
print("0!=1")
else:
fact=1
for i in range(n,0,-1):
fact*=i
print("{0}!={1}".format(n,fact))
2.結果請輸入非負整數n:5
5!=120
while(1):
n=int(input("請輸入非負整數n:"))
if(n>=0):break
if(int(n)==0):
print("0!=1")
else:
fact=1
for i in range(n,0,-1):
fact*=i
print("{0}!={1}".format(n,fact))
2.結果請輸入非負整數n:5
5!=120