就是一个模板，不多说别的了。
#include<bits/stdc++.h> using namespace std; #define ST static #define C const #define int int #define RT return #define OP operator #define LL long long #define B bool #define F friend #define TH this #define V void #define W while struct inf { ST C int mod=100000000; ST C int width=8; B sign; size_t length; vector<int>num; inf(LL x=0){*TH=x;} inf(C string&x){*TH=x;} inf(C inf&x){*TH=x;} V cutLeadingZero(){W(num.back()==0&&num.size()!=1)num.pop_back();} V setLength() { cutLeadingZero(); int tmp=num.back(); if(tmp==0)length=1; else{length=(num.size()-1)*width;W(tmp>0)++length,tmp/=10;} } inf&OP=(LL x) { num.clear(); if(x>=0)sign=1;else{sign=0;x=-x;} do{num.push_back(x%mod);x/=mod;}W(x>0); setLength(); RT*TH; } inf&OP=(C string&str) { num.clear(); sign=(str[0]!='-'); int x,len=(str.size()-1-(!sign))/width+1; for(int i=0;i<len;i++) { int End=str.length()-i*width; int start=max((int)(!sign),End-width); sscanf(str.substr(start,End-start).c_str(),"%d",&x); num.push_back(x); } setLength(); RT*TH; } inf&OP=(C inf&tmp) { num=tmp.num; sign=tmp.sign; length=tmp.length; RT*TH; } size_t size()C{RT length;} inf e(size_t n)C { int tmp=n%width; inf ans; ans.length=n+1; n/=width; W(ans.num.size()<=n) ans.num.push_back(0); ans.num[n]=1; W(tmp--)ans.num[n]*=10; RT ans* (*TH); } inf abs()C { inf ans(*TH); ans.sign=1; RT ans; } C inf&OP+()C{RT*TH;} inf OP+(C inf&b)C { if(!b.sign)RT*TH-(-b); if(!sign)RT b-(-*TH); inf ans; ans.num.clear(); for(int i=0,g=0;;i++) { if(g==0&&i>=num.size()&&i>=b.num.size())break; int x=g; if(i<num.size())x+=num[i]; if(i<b.num.size())x+=b.num[i]; ans.num.push_back(x%mod); g=x/mod; } ans.setLength(); RT ans; } inf OP-()C { inf ans(*TH); if(ans!=0)ans.sign=!ans.sign; RT ans; } inf OP-(C inf&b)C { if(!b.sign)RT*TH+(-b); if(!sign)RT-((-*TH)+b); if(*TH<b)RT-(b-*TH); inf ans; ans.num.clear(); for(int i=0,g=0;;i++) { if(g==0&&i>=num.size()&&i>=b.num.size())break; int x=g; g=0; if(i<num.size())x+=num[i]; if(i<b.num.size())x-=b.num[i]; if(x<0) { x+=mod; g=-1; } ans.num.push_back(x); } ans.setLength(); RT ans; } inf OP*(C inf&b)C { int lena=num.size(),lenb=b.num.size(); vector<LL> ansLL; for(int i=0;i<lena+lenb;i++)ansLL.push_back(0); for(int i=0;i<lena;i++) for(int j=0;j<lenb;j++) ansLL[i+j]+=(LL)num[i]* (LL)b.num[j]; W(ansLL.back()==0&&ansLL.size()!=1)ansLL.pop_back(); int len=ansLL.size(); LL g=0,tmp; inf ans; ans.sign=(ansLL.size()==1&&ansLL[0]==0)||(sign==b.sign); ans.num.clear(); for(int i=0;i<len;i++) { tmp=ansLL[i]; ans.num.push_back((tmp+g)%mod); g=(tmp+g)/mod; } if(g> 0)ans.num.push_back(g); ans.setLength(); RT ans; } inf OP/(C LL&b)C { inf c; c.num.clear(); for(int i=0;i<num.size();i++) c.num.push_back(0); LL g=0; for(int i=num.size()-1;i>=0;i--) { c.num[i]=int((num[i]+g* mod)/b); g=num[i]+g* mod-c.num[i]* b; } for(int i=num.size()-1;c.num[i]==0;i--) c.num.pop_back(); RT c; } inf OP/(C inf&b)C { inf aa((*TH).abs()); inf bb(b.abs()); if(aa<bb)RT 0; char*str=new char[aa.size()+1]; memset(str,0,sizeof(char)*(aa.size()+1)); inf tmp; int lena=aa.length,lenb=bb.length; for(int i=0;i<=lena-lenb;i++) { tmp=bb.e(lena-lenb-i); W(aa>=tmp) { ++str[i]; aa=aa-tmp; } str[i]+='0'; } inf ans(str); delete[]str; ans.sign=(ans==0||sign==b.sign); RT ans; } inf OP%(C LL&b)C { LL ans=0; for(int i=num.size()-1;i>=0;i--)ans=(ans*mod+num[i])%b; RT ans; } inf OP%(C inf&b)C{RT*TH-*TH/b*b;} inf&OP++(){*TH=*TH+1;RT*TH;} inf&OP--(){*TH=*TH-1;RT*TH;} inf&OP+=(C inf&b){*TH=*TH+b;RT*TH;} inf&OP-=(C inf&b){*TH=*TH-b;RT*TH;} inf&OP*=(C inf&b){*TH=*TH*b;RT*TH;} inf&OP/=(C LL&b){*TH=*TH/b;RT*TH;} inf&OP/=(C inf&b){*TH=*TH/b;RT*TH;} inf&OP%=(C LL&b){*TH=*TH%b;RT*TH;} inf&OP%=(C inf&b){*TH=*TH%b;RT*TH;} B OP<(C inf&b)C { if(sign&&!b.sign)RT 0; if(!sign&&b.sign)RT 1; if(!sign&&!b.sign)RT-b<-*TH; if(num.size()!=b.num.size())RT num.size()<b.num.size(); for(int i=num.size()-1;i>=0;i--) if(num[i]!=b.num[i])RT num[i]<b.num[i]; RT 0; } B OP>(C inf&b)C{RT b<*TH;} B OP<=(C inf&b)C{RT!(b<*TH);} B OP>=(C inf&b)C{RT!(*TH<b);} B OP!=(C inf&b)C{RT b<*TH||*TH<b;} B OP==(C inf&b)C{RT!(b<*TH)&&!(*TH<b);} B OP||(C inf&b)C{RT*TH!=0||b!=0;} B OP&&(C inf&b)C{RT*TH!=0&&b!=0;} B OP!(){RT(B)(*TH==0);} F ostream&OP<<(ostream&out,C inf&x) { if(!x.sign)out<<'-'; out<<x.num.back(); for(int i=x.num.size()-2;i>=0;i--) { char buf[10]; sprintf(buf,"%08d",x.num[i]); for(int j=0;j<strlen(buf);j++)out<<buf[j]; } RT out; } F istream&OP>>(istream&in,inf&x) { string str; in>>str; size_t len=str.size(); int start=0; if(str[0]=='-')start=1; if(str[start]==' ') RT in; for(int i=start;i<len;i++) if(str[i]<'0'||str[i]>'9') RT in; x.sign=!start; x=str.c_str(); RT in; } inf pow(int n) { inf ans=1,base=*TH; W(n) { if(n&1)ans=ans*base; base=base*base; n>>=1; } RT ans; } }; int main() { int n; inf ans; ans=1; cin>>n; for(int i=1;i<=n;i++) ans*=i; cout<<ans<<endl; RT 0; }