大数加、减、乘、除、阶乘模板

阶乘

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;

int res[20005];//[0]->个位 
void jiecheng(int n){ //n的阶乘 
  res[0]=1; //个位为1
  int cf=0; //进位为0 
  for (int i=2; i<=n; i++){ //2到n相乘 
    for (int j=0; j<20005; j++){ //res[]中每个元素与i相乘，多位乘1位不会爆int 
      int s = res[j]*i + cf;
      cf = s/10;
      res[j] = s%10;
    } 
  }
  int pos;
  for (int i=20000; i>=0; i--){
    if (res[i]!=0){
      pos=i;
      break;
    }
  }
  for (int i=pos; i>=0; i--){
    printf("%d", res[i]);
  }
}
int main(){
  int n;
  cin>>n;
  jiecheng(n);
  return 0;
}

加、减、乘、除

#include <iostream>
#include <cstdio>
#include <cstring>
#include <string>
#include <algorithm>
using namespace std;

int a[2000], b[2000], c[2000];
void jiafa(string str1, string str2){
//c=a+b
  a[0]=str1.length();
  for (int i=1; i<=a[0]; i++)
    a[i]=str1[a[0]-i]-'0';
  b[0]=str2.length();
  for (int i=1; i<=b[0]; i++)
    b[i]=str2[b[0]-i]-'0';
  
  int len = max(a[0], b[0]);
  for (int i=1; i<=len; i++){
    c[i] += a[i]+b[i];
    c[i+1] = c[i]/10;
    c[i]= c[i]%10;
  }
  len++;
  while (c[len]==0 && len>1)//>1很重要，有可能是0 
    len--;
  for (; len>=1; len--){
    printf("%d", c[len]);
  }
}
int compare_string(string str1, string str2){
  //str1>=str2-->return 0; else return 1;
  if (str1.length()>str2.length())  return 0;
  if (str1.length()<str2.length())  return 1;
  for (int i=0; i<str1.length(); i++){
    if (str1[i]>str2[i])  return 0;
    if (str1[i]<str2[i])  return 1;
  }
  return 0;
}
void jianfa(string str1, string str2){
//c=a-b
  a[0]=str1.length();
  for (int i=1; i<=a[0]; i++)
    a[i]=str1[a[0]-i]-'0';
  b[0]=str2.length();
  for (int i=1; i<=b[0]; i++)
    b[i]=str2[b[0]-i]-'0';
  
  int flag = compare_string(str1, str2);
  if (flag==0){
    for (int i=1; i<=a[0]; i++){
      c[i] = a[i]-b[i];
      if (c[i]<0){
        c[i]+=10;
        c[i+1]-=1;
      }
      int len = a[0]+1;
      while (c[len]==0 && len>1)
        len--;
      for (; len>=1; len--)
        printf("%d", c[len]);
    }
  }else{
    printf("-");
    for (int i=1; i<=b[0]; i++){
      c[i] = b[i]-a[i];
      if (c[i]<0){
        c[i]+=10;
        c[i+1]--;
      }
    }
    int len=b[0]+1;
    while (c[len]==0 && len>1)
      len--;
    for (; len>=1; len--)
      printf("%d", c[len]); 
  }
}
void chengfa(string str1, string str2){
//c=axb
  a[0]=str1.length();
  for (int i=1; i<=a[0]; i++)
    a[i]=str1[a[0]-i]-'0';
  b[0]=str2.length();
  for (int i=1; i<=b[0]; i++)
    b[i]=str2[b[0]-i]-'0';
  
  for (int i=1; i<=a[0]; i++){
    for (int j=1; j<=b[0]; j++){
      c[i+j-1]+=a[i]*b[j];
      c[i+j]+=c[i+j-1]/10;
      c[i+j-1]%=10;
    }
  }
  int len=a[0]+b[0]+1;
  while (c[len]==0 && len>1)
    len--;
  for (; len>=1; len--)
    printf("%d", c[len]); 
}
void chufa_low(string str1, string str2){
//c=a/b
  a[0] = str1.length();
  //注意除法为正序放 
  for (int i=1; i<=a[0]; i++)
    a[i] = str1[i-1]-'0';
  int b = atoi(str2.c_str());
  int x=0;//高位余数 
  
  for (int i=1; i<=a[0]; i++){
    c[i] =(x*10+a[i])/b;
    x=(x*10+a[i])%b; 
  } 
  int len=1;
  while (c[len]==0 && len<a[0])
    len++;
  for (; len<=a[0]; len++)
    printf("%d", c[len]);
}
int compare_string(int a[], int b[]){
  if (a[0]>b[0])  return 0;
  if (a[0]<b[0])  return 1;
  for (int i=a[0]; i>=1; i--){//从高位到低位比较a，b 
    if (a[i]>b[i])  return 0;
    if (a[i]<b[i])  return 1;
  }
  return 0;
}
void sub(int a[], int b[]){
//a = a - b
  for (int i=1; i<=a[0]; i++){
    a[i] = a[i]-b[i];
    if (a[i]<0){
      a[i+1]--;
      a[i]+=10;
    }
  }
  while (a[a[0]]==0 && a[0]>1)
    a[0]--;
}
void chufa_high(string str1, string str2){
//c = a / b
  a[0]=str1.length();
  for (int i=1; i<=a[0]; i++)
    a[i]=str1[a[0]-i]-'0';
  b[0]=str2.length();
  for (int i=1; i<=b[0]; i++)
    b[i]=str2[b[0]-i]-'0';
  
  int tmp[2000];
  c[0]=max((a[0]-b[0]), 0)+1;
  
  for (int i=c[0]; i>=1; i--){
    memset(tmp, 0, sizeof(tmp));
    for (int j=1; j<=b[0]; j++)
      tmp[i+j-1]=b[j];
    tmp[0] = b[0]+i-1;
    
    while (compare_string(a, tmp)==0){
      c[i]++;
      sub(a, tmp);
    }
  }
  //商
  while (c[c[0]]==0 && c[0]>1)
    c[0]--;
  for (int i=c[0]; i>=1; i--)
    printf("%d", c[i]);
  printf("\n");
  //余数
  for (int i=a[0]; i>=1; i--)
    printf("%d", a[i]); 
}
int main(){
  string str1, str2;
  cin>>str1>>str2;
  chufa_high(str1, str2);
  return 0;
}