高精度加减法 1000阶乘求法

1000的阶乘 2568位

#include <iostream.h>
#include <string.h>
#include <stdlib.h>
#include <math.h>
void fun(const char *a,const char *b ,char *c)
{
    int index;
    if (a[0]>'0'&&b[0]>'0')//两个正数相加
    {
        index=0;
    }
    if (a[0]=='-'&&b[0]=='-')//两个负数相加
    {
        index=2;
    }
    if (a[0]>'0'&&b[0]=='-')//a+,b-
    {
        index=1;
    }
    if (a[0]=='-'&&b[0]>'0')
    {
        index=3;
    }
    switch(index)
    {
    case 0:
        {
            int remainder=0;
            int length=strlen(a)>strlen(b)?strlen(a):strlen(b);
            for (int i=strlen(a)-1,j=strlen(b)-1;i>=0||j>=0;i--,j--)
            {
                int x1,x2;
                if (i>=0) 
                    x1=a[i]-'0';
                else
                    x1=0;
                if (j>=0) 
                    x2=b[j]-'0';
                else
                    x2=0;
                div_t temp=div(x1+x2+remainder,10);
                remainder=temp.quot;
                c[length--]=temp.rem+'0';
                
                
            }
            
            if(remainder!=0)
                c[0]=remainder+'0';
            else
            {
                for (int i=0;i<strlen(c);i++)
                {
                    c[i]=c[i+1];
                }
            }
            
        }
        break;
    case 1:
        {
            if (strlen(a)>strlen(b)-1||strlen(a)==strlen(b)-1&&strcmp(a,b+1)>=0)//a-b为+
            {
                int remainder=0;
                for (int i=strlen(a)-1,j=strlen(b)-1;i>=0||j>0;i--,j--)
                {
                    int x1,x2;
                    if (i>=0)
                    {
                        x1=a[i]-'0';
                    } 
                    else
                    {
                        x1=0;
                    }
                    if (j>0)
                    {
                        x2=b[j]-'0';
                    } 
                    else
                    {
                        x2=0;
                    }
                    int value=x1-x2+remainder;
                    if (value>=0)
                    {
                        c[i]=value+'0';
                        remainder=0;
                    } 
                    else
                    { 
                        c[i]=value+10+'0';
                        remainder=-1;
                    }
                }
            } 
            else
            {
                int remainder=0;
                for (int i=strlen(a)-1,j=strlen(b)-1;i>=0||j>0;i--,j--)
                {
                    int x1,x2;
                    if (i>=0)
                    {
                        x1=a[i]-'0';
                    } 
                    else
                    {
                        x1=0;
                    }
                    if (j>0)
                    {
                        x2=b[j]-'0';
                    } 
                    else
                    {
                        x2=0;
                    }
                    int value=x2-x1+remainder;
                    if (value>=0)
                    {
                        c[j]=value+'0';
                        remainder=0;
                    } 
                    else
                    { 
                        c[j]=value+10+'0';
                        remainder=-1;
                    }
                }
                c[0]='-';
            }
            
        }
        break;
    case 2:
        {
            int length=strlen(a)>strlen(b)?strlen(a):strlen(b);
            int remainder=0;
            for (int i=strlen(a)-1,j=strlen(b)-1;i>0||j>0;i--,j--)
            {
                int x1,x2;
                if (i>0) 
                    x1=a[i]-'0';
                else
                    x1=0;
                if (j>0) 
                    x2=b[j]-'0';
                else
                    x2=0;
                div_t temp=div(x1+x2+remainder,10);
                remainder=temp.quot;
                if (i>=j)
                {
                    c[i+1]=temp.rem+'0';
                } 
                else
                {
                    c[j+1]=temp.rem+'0';
                }
            }
            if(remainder!=0)
            {
                c[1]=remainder+'0';
                c[0]='-';
            }
            else
            {
                c[0]='-';
                for (int i=1;i<=length+3;i++)
                {
                    c[i]=c[i+1];
                }
            }
        }
        break;
    case 3:
        {
            if (strlen(b)>strlen(a)-1||strlen(b)==strlen(a)-1&&strcmp(b,a+1)>=0)//b-a为+
            {
                int remainder=0;
                for (int i=strlen(b)-1,j=strlen(a)-1;i>=0||j>0;i--,j--)
                {
                    int x1,x2;
                    if (i>=0)
                    {
                        x1=b[i]-'0';
                    } 
                    else
                    {
                        x1=0;
                    }
                    if (j>0)
                    {
                        x2=a[j]-'0';
                    } 
                    else
                    {
                        x2=0;
                    }
                    int value=x1-x2+remainder;
                    if (value>=0)
                    {
                        c[i]=value+'0';
                        remainder=0;
                    } 
                    else
                    { 
                        c[i]=value+10+'0';
                        remainder=-1;
                    }
                }
            } 
            else
            {
                int remainder=0;
                for (int i=strlen(a)-1,j=strlen(b)-1;i>0||j>=0;i--,j--)
                {
                    int x1,x2;
                    if (i>0)
                    {
                        x1=a[i]-'0';
                    } 
                    else
                    {
                        x1=0;
                    }
                    if (j>=0)
                    {
                        x2=b[j]-'0';
                    } 
                    else
                    {
                        x2=0;
                    }
                    int value=x1-x2+remainder;
                    if (value>=0)
                    {
                        c[i]=value+'0';
                        remainder=0;
                    } 
                    else
                    { 
                        c[i]=value+10+'0';
                        remainder=-1;
                    }
                }
                c[0]='-';
            }
            
        }
        break;
    }
}
void main()
{
    char sum[10000]={'\0'};
    char temp1[10000]={'\0'};
    char temp2[10000]={'\0'};
    sum[0]='1';
    for (int i=2;i<=20;i++)
    {
        memset(temp2,0,10000);
        strcpy(temp2,sum);
        for (int j=1;j<=i-1;j++)
        {
            memset(temp1,0,10000);
            strcpy(temp1,sum);
            fun(temp1,temp2,sum);
            
        }
        cout<<sum<<endl;
    }
    
    
    //cout<<sum<<endl;
    
}