高精度乘法

#include<cstdio>#include<iostream>#include<cstring>#include<algorithm>using namespace std;const int MAXN = 5000;inline int get(){char c;while((c = getchar()) < '0' || c > '9');int cnt = c - '0';while((c = getchar()) >= '0' && c <= '9') cnt = cnt * 10 + c - '0';return cnt;}struct data{int a[MAXN],len;data(int len = 1){memset(a,0,sizeof(a));}data operator * (const data &b){data c;c.len = len + b.len;for(int i = 1; i <= len; i++){for(int j = 1; j <= b.len; j++){c.a[i+j-1] += a[i] * b.a[j];}}for(int i = 1; i <= c.len; i++){if(c.a[i] >= 10){int p = c.a[i] / 10;c.a[i] = c.a[i] - p * 10;c.a[i+1] += p;}}while(c.a[c.len] == 0 && c.len > 1) c.len--;return c;//容易漏 }}a,b; char s1[MAXN],s2[MAXN];int i1,i2;inline bool pd1(){return (s1[i1] >= '0' && s1[i1] <= '9');}inline bool pd2(){return (s2[i2] >= '0' && s2[i2] <= '9');}int main(){/*#ifdef lwy#elsefreopen(".in","r",stdin);freopen(".out","w",stdout);#endif*/scanf("%s %s",s1,s2); // s1+1 , s2+1 的输入方式无法使用strlen函数 （即从s[1]位置开始读入） a.len = strlen(s1);b.len = strlen(s2);i1 = 0; i2 = 0;if(s1[0] == '0' || s2[0] == '0'){printf("0");return 0;}//答案为 0 时 不应有"-" if(!pd1() && pd2()){printf("-");i1++;}if(pd1() && !pd2()){printf("-");i2++;}if(!pd1() && !pd2()){i1++; i2++;}for(int i = a.len - 1; i >= i1; i--){a.a[a.len - i] = s1[i] - '0';}a.len = a.len - i1;for(int i = b.len - 1; i >= i2; i--){b.a[b.len - i] = s2[i] - '0';}b.len = b.len - i2;a = a * b;for(int i = a.len; i >= 1; i--){printf("%d",a.a[i]);}return 0;}

补充：高精度除法中高精除高精通常采用减法模拟除法，对每一位被除数都减去除数，一直减到当前位置的数字（包含前面的余数）小于除数（由于每一位都小于10，所以最多进行10次计算），高精除低精可以直接除。