温度转换循环

while True:
    a = int(input('摄氏度转换为华氏度请按1\n华氏度转换为摄氏度请按2\n退出请按3\n'))
    if a==1:
        c = float(input('请输入摄氏度:'))
        f = c*9/5+32
        print('摄氏{:.2f}的华氏度为{:.2f}'.format(c,f))
    elif a==2:
        f = float(input('请输入华氏度:'))
        c = 5/9*(f-32)
        print('华氏{:.2f}的摄氏度为{:.2f}'.format(f,c))
    else:
        break