大整数运算

高精度加减乘除

#include<stdio.h>
#include<string.h>
struct bign {
	int b[1000];
	int len;
	bign() {
		memset(b, 0, sizeof(b));
		len = 0;
	}
};
bign change(char str[]) {
	bign a;
	a.len = strlen(str);
	for (int i = 0; i < a.len; i++) {
		a.b[i] = str[a.len - i - 1]-'0';
	}
	return a;
}
bign add(bign a, bign b) {
	bign c;
	int carry = 0;
	for(int i=0;i<a.len||i<b.len;i++){
		int temp = a.b[i] + b.b[i] + carry;
		c.b[c.len++] = temp % 10;
		carry = temp / 10;
	}
	if (carry != 0) {
		c.b[c.len++] = carry;
	}
	return c;
}
bign sub(bign a, bign b) {
	bign c;
	int carry = 0;
	for (int i = 0; i < a.len || i < b.len; i++) {
		if (a.b[i] < b.b[i]) {
			a.b[i + 1]--;
			a.b[i] += 10;
		}
		c.b[c.len++] = a.b[i] - b.b[i];
	}
	while (c.len - 1 >= 1 && c.b[c.len - 1] == 0) {
		c.len--;
	}
	return c;
}
bign multi(bign a,int d) {
	bign c;
	int carry = 0;
	for (int i = 0; i < a.len ; i++) {
		int temp = a.b[i] * d + carry;
		c.b[c.len++] = temp % 10;
		carry = temp / 10;
	}
	while (carry != 0) {
		c.b[c.len++] = carry % 10;
		carry = carry / 10;
	}
	return c;
}
bign divide(bign a, int b, int& r) {
	bign c;
	c.len = a.len;
	for(int i=a.len-1;i>=0;i--)
	{
		r = r * 10 + a.b[i];
		if (r < b) c.b[i] = 0;
		else {
			c.b[i] = r / b;
			r %= b;
		}
	}
	while (c.len - 1 >= 1 && c.b[c.len - 1] == 0) {
		c.len--;
	}
	return c;
}
void print(bign a) {
	for (int i = a.len - 1; i >= 0; i--) {
		printf("%d", a.b[i]);
	}
	printf("\n");
}
int main()
{
	int r = 0; //除法最后的余数
	char str1[1000],str2[1000];
	scanf("%s%s", str1, str2);
	bign a = change(str1);
	bign b = change(str2);
	print(add(a, b)); //加
	print(sub(a, b)); //减
	print(multi(a, 10));  //乘
	print(divide(a, 10, r));  //除
}