willsun888
9/18/2013 - 2:52 PM

## 大整数运算

``````//大整数运算
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

//字符串反转
void strrev(char* s)
{
int i=-1;
while(s[++i]!='\0');
for(int j=0;j<i/2;j++){
char tmp = s[j];
s[j] = s[i-j-1];
s[i-j-1]=tmp;
}
}
void Add(const char*str1, const char* str2, char* ans)
{
int l1, l2, l;
l1 = strlen(str1);
l2 = strlen(str2);
l = l1>l2 ? l1 : l2;
char* s1 = (char*)malloc(sizeof(char)*(l1+1));
char* s2 = (char*)malloc(sizeof(char)*(l2+1));
memcpy(s1,str1,(l1+1)*sizeof(char));
memcpy(s2,str2,(l2+1)*sizeof(char));
strrev(s1);
strrev(s2);
int i;
int sum, carry;
i=sum=carry=0;
while(i<l){
char a = i<l1?s1[i]:'0';
char b = i<l2?s2[i]:'0';
sum = a-'0'+b-'0' + carry;
ans[i] = sum % 10 + '0';
carry = sum / 10;
i++;
}
if(carry!=0)
ans[i++]=carry+'0';
ans[i]='\0';
strrev(ans);
free(s1);
free(s2);
}
void Mul(const char*str1, const char* str2, char* ans)
{
int l1, l2, l;
l1 = strlen(str1);
l2 = strlen(str2);
l = l1 + l2;
ans[0]='\0';
char* s1 = (char*)malloc(sizeof(char)*(l1+1));
char* s2 = (char*)malloc(sizeof(char)*(l2+1));
memcpy(s1,str1,(l1+1)*sizeof(char));
memcpy(s2,str2,(l2+1)*sizeof(char));
strrev(s1);
strrev(s2);
char* tmp = (char*)malloc(sizeof(char)*(l1+2));
int s, carry;
s = carry = 0;
for(int i=0;i<l2;i++){
int j;
for(int j=0;j<i;j++)
tmp[j]='0';
for(j=0;j<l1;j++){
s = (s1[j]-'0')*(s2[i]-'0')+carry;
tmp[i+j]=s%10+'0';
carry=s/10;
}
if(carry!=0)
tmp[i+j++]=carry+'0';
tmp[i+j]='\0';
strrev(ans);
strrev(tmp);
strrev(ans);
}
strrev(ans);
}
int main()
{
const char a[] = "12345";
const char b[] = "123";
char c[1024];