高精度乘法加强

Posted 2020-09-24 jhcelue

转自http://blog.csdn.net/cm_yali/article/details/50607751

#include<stdio.h>  
#include<stdlib.h>  
#include<string.h>  
char s[30001];  
long long a[15000],b[15000],c[50001];  
int main ()  
{  
    int alen,blen,clen;  
    int i,j,k,m,n;   
    gets(s);  
    alen=strlen(s);  
    k=0;  
    for(i=alen-1;i>=0;i-=3){  
        long long tmp=0;  
        int start;  
        start=i-2;  
        if(start<0)start=0;  
        for(j=start;j<=i;j++)  
            tmp=tmp*10+s[j]-'0';  
        a[++k]=tmp;  
    }  
    alen=k;  
       
    gets(s);  
    blen=strlen(s);  
    k=0;  
    for(i=blen-1;i>=0;i-=3){  
        long long tmp=0;  
        int start;  
        start=i-2;  
        if(start<0)start=0;  
        for(j=start;j<=i;j++)  
            tmp=tmp*10+s[j]-'0';  
        b[++k]=tmp;  
    }  
    blen=k;  
       
    for(i=1;i<=alen;i++)  
        for(j=1;j<=blen;j++)  
            c[i+j-1]+=a[i]*b[j];  
    clen=alen+blen;            
    while(c[clen]==0 && clen>1)  
        clen--;                               
    for(i=1;i<clen;i++)  
        if(c[i]>=1000){  
            c[i+1]+=c[i]/1000;  
            c[i]%=1000;  
            }  
    printf("%lld",c[clen]);  
    for(i=clen-1;i>=1;i--){  
        if(c[i]<10)printf("00");  
        else if(c[i]<100)printf("0");  
        printf("%lld",c[i]);}  
    return 0;  
}