Question

value = input("Enter the binary value to convert to a decimal number.")
prod = 0
power = 0
ans = 0
for i in range (int(value)):
    prod = ((int(value[*right most digit here*])) * ((2**power)))
    ans = prod + ans
    prod = 0
    power + 1
else:
    print (ans)

I am trying to create a binary calculator.

I believe I have the power part of the equation working as it begins with 2 ^ 0, then 2 ^ 1 for the next digit and so on. But I am having trouble getting the first part of the equation, the right most digit of the value inputted.

So let's say, 0101 was inputted. I want 1 * ( 2 ^ 0 ) in the first loop, 0 * ( 2 ^ 1) in the second loop, and so on; right to left. So with how indexing works in Python, how can I reverse index it so [4] is in the first loop, then [3] in the second loop, and so on.

Thanks for help.

Answer 1

实现这一目标的更简单方法是将base设为int()为2。例如：

>>> num = '110'
>>> int(num, 2)
6

如果您正在寻找自定义解决方案，您可以创建一个函数：

def binary_string_to_int(binary_string):
    int_num = 0
    for i in binary_string:
        int_num += int(i)
        int_num *= 2
    return int_num / 2

示例运行：

>>> binary_string_to_int('111')
7
>>> binary_string_to_int('101')
5

Answer 2

您的代码中存在一些错误，因此请将其替换为：

value = input("Enter the binary value to convert to a decimal number: ")
value = int(value) # conversion from string to number

power = 0
ans   = 0

while(value > 0):
    lastDigit = value %  10  # last digit
    value     = value // 10  # cutting off last digit (for next iteration)

    prod      = lastDigit * (2 ** power)

    ans       = prod  + ans
    power     = power + 1

print (ans)

最后一位数被计算为除以10之后的余数（value % 10）并且整数除以10（value // 10） - 与基础学校的一年级一样：27 % 10 = 7 27 // 10 = 2

Answer 3

value = input("Enter the binary value to convert to a decimal number.")
power = 0
ans = 0

for i in reversed(value):
    prod = int(i) * (2**power)
    ans = prod + ans
    power += 1
else:
    print(ans)

改进代码，同时尽可能保持代码尽可能接近代码。你的for循环正在创建一个1 to whatever the value we input的列表，这不是你应该做的。一种方法是将输入视为一个字符串（基本上是一个可以迭代的列表）反转它，这样你就可以从右到左，然后对每个值进行操作。您试图获取值输入位置的索引吗？为什么？ Python非常漂亮，你很可能不需要直接告诉索引。

value = input("Enter the binary value to convert to a decimal number.")
prod = 0
power = 0
ans = 0
for i in range(int(len(value))-1):
    prod = ((int(value[-1])) * ((2**power)))
    ans = prod + ans
    prod = 0
    power + 1
else:
    print (ans)

您正在执行值的范围而不是输入len，因此我们使用len()来获取输入的字符串的长度。 -1是因为输入001的字符串长度可以是3，但如果索引3超出范围，因为索引从0开始而不是1

请注意，在Python中，接受负索引值。负指数意味着从列表的末尾开始并向后计数，所以我认为这是您正在寻找的答案。

例如，如果我们有列表my_list=['a','b','c']并且我们致电my_list[-2]，则会返回'b'

Answer 4

然而，有更好的选择，我假设你正在清除你的基础知识。以下可以是选项：

注意：你应该在循环中使用len（value）而不是int（value）。

#  1. When starting the loop from 0 (i.e. i=0). you can use ( len(value) - i )th index.'

for i in range (len(value)):
   prod = ((int(value[len(value) - i - 1])) * ((2**power)))
   ans = prod + ans
   prod = 0
   power = power + 1



# 2. Python also supports negative indexing, So you may run a loop from -1 to -len(value).

for i in range (-1,-len(value) - 1,-1):
   prod = ((int(value[i])) * ((2**power)))
   ans = prod + ans
   prod = 0
   power = power + 1


# 3. You can reverse the whole string in your first step and then loop from 0 to len(value)-1.

value = reversed(value)
for i in range (len(value)):
   prod = ((int(value[i])) * ((2**power)))
   ans = prod + ans
   prod = 0
   power = power + 1

但是代码中存在一些错误（或者可能缺少信息）。此代码仅适用于无符号整数。如果您希望它也可以使用带符号的数字，则必须考虑2的补码。下面是一个非常简单的代码，也可以使用带符号的数字（如果需要）：

#convert binary string into decimal value. Works on 2's complement.
def binToDecimal(s):

    neg = False
    if s[0] == '1':
        s = twosComp(s)
        neg = True
    #compute the decimal value
    val = reduce(lambda x,y : int(x)*2+1 if y=='1' else int(x)*2,'0'+s)
    #negate the value if the first bit is 1
    return -val if neg else val


#return the 2's complement string
def twosComp(s):
    s = list(s[::-1])
    #take 1's complement
    s = ['1' if i=='0' else '0' for i in s]
    #take 2's complement
    for i in range(len(s)):
        if s[i] == '0':
            #no carry will be generated in this case, so we break it.
            s[i] = '1'
            break
        else:
            s[i]='0'

    # return 2's complement string
    return ''.join(map(str,s))[::-1]

How can I reverse index and -1 each loop

4 个答案: