High precision

topic

Detailed

For details, please see the big brother blog: link

1. First read in with a character array, and then reverse the numbers into an integer array.
2. Multiply without carry.
3. Carry
4. Remove the leading 0 (for example, 0X100, the result is 000)
5. Reverse output

Code

#include<bits/stdc++.h>
using namespace std;
const int maxn =2000;
char a[maxn],b[maxn];
int aa[maxn],bb[maxn],c[maxn];
void slove(char a[],char  b[]){
    
    
	int la = strlen(a);
	int lb = strlen(b);
	//逆序进入整形数组 
	for(int i = 1;i<=la;i++){
    
    
		aa[i] = a[la-i]-'0';
	}
	for(int i = 1;i<= lb;i++){
    
    
		bb[i] = b[lb-i] -'0';
	}
	//不进位相乘 
	for(int i = 1;i<=la;i++){
    
    
		for(int j = 1;j<=lb;j++){
    
    
			c[i+j-1]  += aa[i] * bb[j];
		}
	} 
	//进位
	for(int i = 1;i< la + lb;i++){
    
    
		if(c[i] > 9){
    
    
			c[i+1] += c[i]/10;
			c[i]%=10;
		}
	} 
	//除去前导0 
	int len = la + lb;
	while(c[len] ==0 && len > 1)
		len --;
	//倒序输出 
	for(int i =len;i>=1;i--){
    
    
		cout<<c[i];
	}
	
}
int main(){
    
    
	cin>>a>>b;
	slove(a,b);
	return 0;
}