大数四则运算（C语言实现）

大数加法

/***洛谷P1601 A+B Problem（高精）***/
#include
#include
#include

#define maxn 10005

char num1[maxn], num2[maxn];
int _num1[maxn], _num2[maxn];

int _max(int a, int b){
    return a > b ? a : b;
}
void _add(char a[], char b[]){
    int i, j;
    int l_1 = strlen(a);
    int l_2 = strlen(b);
    int len = _max(l_1, l_2);
    for(i = l_1 - 1, j = 0; i >= 0; i--, j++){
        _num1[j] = (int)(a[i] - '0');
    }
    for(i = l_2 - 1, j = 0; i >= 0; i --, j++){
        _num2[j] = (int)(b[i] - '0');
    }
    _num1[len] = 0;
    for(i = 0; i <= len; i++){
        _num1[i] += _num2[i];
        if(_num1[i] > 9){
            _num1[i] %= 10;
            _num1[i + 1]++;
        }
    }
    if(_num1[len] > 0){
        len++;
    }
    for(i = len - 1, j = 0; i >= 0; i--, j++){
        num1[j] = (char)('0' + _num1[i]);
    }
    num1[len] = '\0';
}
int main()
{
    scanf("%s%s", num1, num2);
    _add(num1, num2);
    printf("%s\n", num1);
    return 0;
}

大数减法

/***洛谷P2142 高精度减法***/
#include
#include
#include

#define maxn 10005

char num1[maxn], num2[maxn];
int _num1[maxn], _num2[maxn];

int _max(int a, int b){
    return a > b ? a : b;
}
int cmp(char a[], char  b[]){
    int l_a = strlen(a);
    int l_b = strlen(b);
    if(l_a > l_b) return 1;
    else if(l_a < l_b) return 0;
    else{
        int i;
        for(i = 0; i < l_a; i++){
            if(a[i] > b[i]) return 1;
            else if(a[i] < b[i]) return 0;
        }
        return 2;
    }
}
void _sub(char a[], char b[]){
    int l_a = strlen(a);
    int l_b = strlen(b);
    int len = _max(l_a, l_b);
    int i, j;
    memset(_num1, 0, sizeof(_num1));
    memset(_num2, 0, sizeof(_num2));
    for(i = l_a - 1, j = 0; i >= 0; i--, j++){
        _num1[j] = (int)(a[i] - '0');
    }
    for(i = l_b - 1, j = 0; i >= 0; i--, j++){
        _num2[j] = (int)(b[i] - '0');
    }
    for(i = 0; i < len; i++){
        if(_num1[i] >= _num2[i]){
            _num1[i] -= _num2[i];
        }
        else{
            _num1[i] = (_num1[i] + 10 - _num2[i]);
            _num1[i + 1]--;
        }
    }
    for(i = len - 1; i >= 0; i--){
        if(_num1[i] != 0) break;
    }
    len = i + 1;
    for(i = len - 1, j = 0; i >= 0; i--, j++){
        num1[j] = (char)('0' + _num1[i]);
    }
    num1[len] = '\0';
}
int main()
{
    scanf("%s%s", num1, num2);
    int tag = cmp(num1, num2);
    if(tag == 2) puts("0");
    else if(tag == 1){
        _sub(num1, num2);
        printf("%s\n", num1);
    }
    else{
        _sub(num2, num1);
        printf("-%s\n", num1);
    }
    return 0;
}

大数乘法

/***洛谷P1303 A*B Problem***/
#include
#include
#include

#define maxn 4005

char num1[maxn], num2[maxn];
int _num1[maxn], _num2[maxn], res[maxn];

void _mul(char a[], char b[]){
    int l_a = strlen(a);
    int l_b = strlen(b);
    int i, j;
    for(i = l_a - 1, j = 0; i >= 0; i--, j++){
        _num1[j] = (int)(num1[i] - '0');
    }
    for(i = l_b - 1, j = 0; i >= 0; i--, j++){
        _num2[j] = (int)(num2[i] - '0');
    }
    for(i = 0; i < l_a; i++){
        for(j = 0; j < l_b; j++){
            res[i + j] += _num1[i] * _num2[j];
        }
    }
    for(i = 0; i < l_a + l_b; i++){
        if(res[i] >= 10){
            res[i + 1] += (res[i] / 10);
            res[i] %= 10;
        }
    }
    int len;
    for(i = l_a + l_b; i >= 0; i--){
        if(res[i] != 0){
            len = i + 1;
            break;
        }
    }
    if(i == -1){
        num1[0] = '0'; num1[1] = '\0'; return;
    }
    for(i = len - 1, j = 0; i >= 0; i--, j++){
        num1[j] = (char)('0' + res[i]);
    }
    num1[len] = '\0';
}
int main()
{
    scanf("%s%s", num1, num2);
    _mul(num1, num2);
    printf("%s\n", num1);
    return 0;
}