添加两个大数字作为字符串

Question

我不会在此处添加 "real" 代码片段，因为我尝试了很多变体 - 并取得了不同程度的成功 - 所以我将使用类似 C 的伪代码。

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我想加两个超过ANSI C最大long long的数（比如两个50位的数）

我的想法是，我将使用两个 char[] 数组，并通过将两个加数的每个字符转换为整数，添加并携带十位，然后分配来进行经典的纸笔式加法结果再次作为 char 到 char[] 数组。

我运行遇到的问题是将 char 转换为 int（总是失败）...然后将结果添加到另一个文本数组。尝试使用 result[i] = "5" 或什至其 ascii 值 result[i] = 53 向 char result[] 添加字符总是失败。

伪代码

int add(char *n1, char *n2){
    // examples (Intentionally not the same length)
    // n1     = "12345678901234567890"
    // n2     =      "987654321098765"
    char result[100]; // array for resulting added ints as char
    int r = 100; // The index (set to end) for the result array 
    result[r] = 0; // Assign the char-halt to END of the result
    int carry = 0; //  for carrying the 10s
    maxlength = <length of largest addend> // (sizeof(n)/sizeof(n[0])) doesnt work because pointers

    // start at end (right end) of arrays and move towards start (left end)
    // each loop takes one character, starting at the far RIGHT (end) of the string array
    // i = (maxlength - 1) to skip stop "0"
    for (int i = (maxlength - 1); i >= 0; i--) { 
        a1 = int()n1[i] // doesnt return correct value in tests. Neither does a1 = n1[i]-0
        a2 = int()n1[i] // doesnt return correct value in tests. Neither does a1 = n1[i]-0
        int asum = a1 + a2 + carry

        // carry all the tens
        carry = 0; // reset carry
        while (asum > 10){
            carry += 10; 
            asum -= 10; 
        }
        result[r] = char()asum 
        r -= 1 // Move result index one to the LEFT
    }
}

Answer 1

The problems I'm running into is converting the char to int ...

C 标准保证 '0' 到 '9' 的 10 个字符保持连续递增的值：

5.2.1 Character sets

[...]

3 Both the basic source and basic execution character sets shall have the following members: the 10 decimal digits

0 1 2 3 4 5 6 7 8 9

[...] the value of each character after 0 in the above list of decimal digits shall be one greater than the value of the previous.

看看这个，了解一下概念：

#include stdio.h>

int main(void)
{
  char c = '7'; 
  int i = c - '0'; 

  printf("c = %c, i = %d\n", c, i); 
}

添加两个大数字作为字符串

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