10000位内高精度乘法（大数乘法）1…

大整数乘法.模拟小学生算数.#include <stdio.h>#include <string.h>#define size 10000+2#define truesize size-1-1int ans[size*size*100]={0};int multiply(char a[size],int sa,char b[size],int sb){ int i,j,k,pa,pb,ec=0; long last=0; for(i=0;(pa=truesize-i)>=sa;i++){  long cp=0;  for(j=0;(pb=truesize-j)>=sb;j++){   int na=a[pa]-'0';   int nb=b[pb]-'0';   cp=cp+na*nb;   ans[ec=truesize-i-j]+=cp;   cp/=10;     }  while(cp&&ec-1){   ans[--ec]+=cp;   cp/=10;  } } ec=truesize; last=0; while(ec>=0){  last+=ans[ec];  ans[ec--]=last;  last/=10; } for(i=0;i<=truesize;i++) if(ans[i])break; return i;}int read(char c[size]){ int l=0,i; char t[size]=""; c[truesize+1]='\0'; while(t[l]=getchar()){  if(t[l]=='\n'||t[l]==' '){   l--;   break;  }  l++; } for(i=0;i<=l;i++) c[truesize-(l-i)]=t[i]; return truesize-l;}void show(int i){ if(i<=truesize) for(;i<=truesize;i++) printf("%d",ans[i]); else printf("%d",0); printf("\n");}int main(){ char a[size]=""; char b[size]=""; int sa=read(a); int sb=read(b); int sc=multiply(a,sa,b,sb); show(sc); return 0;}