C语言 · 大数乘法

 1 #include<stdio.h>
 2 #include<string.h>
 3 char s[1000];
 4 void mult(char a[],char b[])
 5 {
 6     int i,j,k=0,alen,blen,sum=0,res[500][500]={0},flag=0;
 7     char result[500];
 8     alen=strlen(a);blen=strlen(b); 
 9 
10     for (i=0;i<alen;i++)
11     for (j=0;j<blen;j++) res[i][j]=(a[i]-'0')*(b[j]-'0');
12 
13     for (i=alen-1;i>=0;i--)
14         {
15             for (j=blen-1;j>=0;j--) sum=sum+res[i+blen-j-1][j];
16             result[k]=sum;
17             k=k+1;
18             sum=sum/10;
19         }
20 
21     for (i=blen-2;i>=0;i--)
22         {
23             for (j=0;j<=i;j++) sum=sum+res[i-j][j];
24             result[k]=sum;
25             k=k+1;
26             sum=sum/10;
27         }
28     if (sum!=0) {result[k]=sum;k=k+1;}
29 
30     for (i=0;i<k;i++) result[i]+='0';
31     for (i=k-1;i>=0;i--) s[i]=result[k-1-i];
32     s[k]='';
33 
34     while(1)
35         {
36         if (strlen(s)!=strlen(a)&&s[0]=='0') 
37             strcpy(s,s+1);
38         else
39             break;
40         }
41 }
42 int main(){
43     char str1[1000],str2[1000];
44     int t,frag,i;
45 //    while(scanf("%s%s",str1,str2)!=EOF){
46     scanf("%s%s",str1,str2); 
47     mult(str1,str2);
48     frag=0;
49     t=strlen(s);
50     for(i=0;i<t;i++){
51         if(s[i]!='0')
52             frag=1;
53         if(frag==1)
54             printf("%c",s[i]);
55     }
56     if(frag==0)
57         printf("0");
58 //    }
59     return 0;
60 }