高精度

1，阶乘的准确值为了方便起见，我们F[0]保存个位，f[1]保存十位，f[2]保存百位·······，只需模拟手算即可完成n！。在输出时忽略前导0.#include <iostream>#include <string>#include <cstring>using namespace std;const int maxn=3000;int f[maxn];int main(){int i, j, n;cin>>n;memset(f, 0, sizeof(f));f[0]=1;for(i=2; i<=n; i++){int c=0; for(j=0; j<maxn; j++){int s=f[j]*i+c;f[j]=s%10;c=s/10;}}//忽略前导0 for(j=maxn-1; j>=0; j--){if(f[j])break;}for(i=j; i>=0; i--)cout<<f[i];cout<<endl;return 0;}2，高精度运算类bign设计一个结构体bign来储存高精度非负整数const int maxn =1000;struct bign{int len, s[maxn];bign(){memset(s, 0, sizeof(s));len=1;}}；然后是重新定义赋值运算符：const int maxn =1000;struct bign{int len, s[maxn];bign(){memset(s, 0, sizeof(s));len=1;}bign operator = (const char* num){len=strlen(num);for(int i=0; i<len; i++)s[i]=num[len-i-1]-'0';return *this;｝}；这样就可以用x=“1234567898765432123456789”这样的方式给x赋值了，它会把这个字符串转化为逆序数组加长度的内部表示方法。为了让其也支持x=1234，这样的赋值方式，另外一种赋值运算是：const int maxn =1000;struct bign{int len, s[maxn];bign(){memset(s, 0, sizeof(s));len=1;}bign operator = (const char* num){len=strlen(num);for(int i=0; i<len; i++)s[i]=num[len-i-1]-'0';return *this;｝bign operator = (int num){char s[maxn];sprintf(s, "%d", num);*this=s;return *this;｝}；为了让代码支持初始化操作，还需要增加两个函数：const int maxn =1000;struct bign{int len, s[maxn];bign(){memset(s, 0, sizeof(s));len=1;}bign(int num){*this=num;}bign(const char* num){*this=num;}bign operator = (const char* num){len=strlen(num);for(int i=0; i<len; i++)s[i]=num[len-i-1]-'0';return *this;｝bign operator = (int num){char s[maxn];sprintf(s, "%d", num);*this=s;return *this;｝}；然后提供一个函数将其转化为字符串：const int maxn =1000;struct bign{int len, s[maxn];bign(){memset(s, 0, sizeof(s));len=1;}bign(int num){*this=num;}bign(const char* num){*this=num;}string str() const{string res="";for(int i=0; i<len; i++)res=(char)(s[i]+'0')+res;if(res=="")res=0;return res;}bign operator = (const char* num){len=strlen(num);for(int i=0; i<len; i++)s[i]=num[len-i-1]-'0';return *this;｝bign operator = (int num){char s[maxn];sprintf(s, "%d", num);*this=s;return *this;｝}；接下来重载<<和>>符：const int maxn =1000;struct bign{int len, s[maxn];bign(){memset(s, 0, sizeof(s));len=1;}bign(int num){*this=num;}bign(const char* num){*this=num;}string str() const{string res="";for(int i=0; i<len; i++)res=(char)(s[i]+'0')+res;if(res=="")res=0;return res;}bign operator = (const char* num){len=strlen(num);for(int i=0; i<len; i++)s[i]=num[len-i-1]-'0';return *this;｝bign operator = (int num){char s[maxn];sprintf(s, "%d", num);*this=s;return *this;｝}；istream& operator >> (istream &in, bign& x){string s;in>>s;x=s.c_str();return in;}ostream& optreator << (ostream &out, const bign& x){out<<x.str();return out;}以此类推可以重载bign的常用运算符