Question

int getFirstValue(string number){
    int result; //holds the converted value
    int total = 0; //holds the sum
    int count = 1;
    // iterate through every character in the string
    for (unsigned i = 0; i < number.length(); i++){  
        if (count % 2 == 0){
            result = number[i] - '0'; //convert the character into an int
            result *= 2; //multiply the value by 2
            total += result; // assign it to total
            ++count; //increment count
        }
    }
    return total; //return the sum
}

我想计算每两位数乘以2的总和。我不知道如何遍历数字，所以我选择将其作为字符串输入然后转换数字。当我尝试每一个数字它工作得很好，但当我使用计数变量它返回0.也许这是一个愚蠢的问题，但我无法弄清楚。怎么了？

Answer 1

您的count变量只会在if (count % 2 == 0)语句的末尾递增。在循环之前count = 1，条件count % 2 == 0将永远不会被验证，total将保持为0直到结束。

您应该在每次迭代时增加count：

for (unsigned i = 0; i < number.length(); i++){  
    if (count % 2 == 0){
        result = number[i] - '0'; //convert the character into an int
        result *= 2; //multiply the value by 2
        total += result; // assign it to total
    }
    ++count; // HERE
}

请注意，count将始终等于i+1。

Answer 2

以下可能有所帮助（我不确定你要求哪些数字，例如，团结，数百......）

int sum(int n)
{
    int res = 0;
    while (n != 0) {
        res += n % 10;
        n /= 100;
    }
    return 2 * res;
}

int sum(const std::string& n)
{
    int res = 0;
    for (std::size_t i = 0; i < n.size(); i += 2) {
        res += *(n.rbegin() + i) - '0';
    }
    return 2 * res;
}

Live example

逐个访问字符

2 个答案: