C++实现大数乘法算法代码
C++实现大数乘法算法代码
//大数乘法算法
#include<iostream>
#include<string>
#include<cstring>
usingnamespacestd;
intmain()
{
stringnum1,num2;
cin>>num1>>num2;
//cout<<num1.size()<<""<<num2.size()<<endl;
constchar*n1;
constchar*n2;
if(num1.size()<num2.size())
{
n1=num2.c_str();
n2=num1.c_str();
}
else
{
n1=num1.c_str();
n2=num2.c_str();
}
char*n=newchar[strlen(n1)+strlen(n2)+1];
for(unsignedinti=0;i<strlen(n1)+strlen(n2);i++)
n[i]='0';
n[strlen(n1)+strlen(n2)]='\0';
//cout<<strlen(n)<<endl;
intcount=0,flag=0;
for(inti=strlen(n1)-1;i>=0;i--)
{
flag++;
intx1=n1[i]-'0';
//cout<<"n1["<<i<<"]为："<<x1<<endl;
charcarry='0';
for(intj=strlen(n2)-1;j>=0;j--)
{
intx2=n2[j]-'0';
//cout<<"n2["<<j<<"]为："<<x2<<endl;
//cout<<"当前位未改变前值为:"<<n[count]<<endl;
intsum=x1*x2+(carry-'0')+n[count]-'0';
//cout<<"sumis"<<sum<<endl;
n[count++]=(sum%10)+'0';
carry=(sum/10)+'0';
//cout<<"当前位的值为:"<<n[count-1]<<endl;
//cout<<"carry的值为："<<carry<<endl;
}
if(carry!='0')
{
n[count]=carry;
count=flag;
//cout<<"当前位的值为:"<<n[count]<<endl;
}
else
count=flag;
}
for(inti=strlen(n)-1;i>=0;i--)
{
if((i==strlen(n)-1)&&(n[i]=='0'))
continue;
cout<<n[i];
}
cout<<endl;
delete[]n;
system("pause");
return0;
}
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