1. #include <stdio.h>
    2. #include <string.h>
    3. #define MAX 500
    5. void reverse(char a[]){
    6.     char temp;
    7.     int len = strlen(a), i;
    8.     for(i = 0; i < (len+1)/2; i++){
    9.         temp = a[i];
    10.         a[i] = a[len-i-1];
    11.         a[len-i-1] = temp;
    12.     }
    13. }
    15. void func(char num1[], char num2[]){
    16.     int l1 = strlen(num1), l2 = strlen(num2);
    17.     //让p1、p2指向数字末尾
    18.     char *p1 = &num1[l1-1], *p2 = &num2[l2-1];
    19.     char result[MAX], *p3 = result;
    20.     //是否需要借位
    21.     int n = 0;
    22.     int rn1, rn2;
    23.     while (p1 >= num1 || p2 >= num2){
    24.         //获取真实数值
    25.         if(p1 >= num1){
    26.             rn1 = *p1 - '0';
    27.             p1--;
    28.         }else{
    29.             rn1 = 0;
    30.         }
    31.         if(p2 >= num2){
    32.             rn2 = *p2 - '0';
    33.             p2--;
    34.         }else{
    35.             rn2 = 0;
    36.         }
    37.         *p3 = (10 + rn1 - rn2 - n) % 10 + '0';
    38.         if(rn1-n < rn2){
    39.             n = 1;
    40.         }else{
    41.             n = 0;
    42.         }
    43.         p3++;
    44.     }
    45.     *p3 = '\0';
    46.     while (1){
    47.         if(*--p3 == '0' && p3 != result){
    48.             *p3 = '\0';
    49.         }else{
    50.             break;
    51.         }
    52.     }
    53.     reverse(result);
    54.     printf("%s\n", result);
    55. }
    57. void BigNumSub(char num1[], char num2[]){
    58.     int len;
    59.     if(strlen(num1) == strlen(num2)){
    60.         len = strlen(num1);
    61.         if(num1[len-1] > num2[-1]){
    62.             func(num1, num2);
    63.         } else{
    64.             func(num2, num1);
    65.         }
    66.     }else if(strlen(num1) > strlen(num2)){
    67.         func(num1, num2);
    68.     }else{
    69.         func(num2, num1);
    70.     }
    71. }
    75. int main(int argc, char *argv[]) {
    76.     BigNumSub("10113", "1013421");
    77.     return 0;
    78. }