算法学习（一）（大数运算）

//大数相减
#include <cstdio>
#include <cstring>
#include <string>
#include <iostream>
#include <cmath>
#include <algorithm>
using namespace std;
int x[100]={0},y[100]={0},z[100]={0};
void sub(int x[],int y[],int len)
{
	for(int i=0;i<len;i++)
	{
		if(x[i]>=y[i]) z[i]=x[i]-y[i];
		else if(x[i]<y[i])
		{
			z[i]=x[i]+10-y[i];
			x[i+1]=x[i+1]-1;
		}
	}
	for(int i=len-1;i>0;i--)
	{
		if(z[i]==0) len--;
		else break;
	}
	for(int i=len-1;i>=0;i--) cout<<z[i];
	cout<<endl;
}
int main()
{
	char chr1[100],chr2[100];
	int len1,len2;
	while(scanf("%s %s",chr1,chr2))
	{
		
		int i,j=0,k=0;
		len1=strlen(chr1);
		len2=strlen(chr2);
		for(i=len1-1,j=0;i>=0;i--) x[j++]=chr1[i]-‘0‘;
		for(i=len2-1,k=0;i>=0;i--) y[k++]=chr2[i]-‘0‘;
		if(len1>len2) sub(x,y,len1);
		else if(len1<len2) 
		{
			printf("-");
			sub(y,x,len2);
		}
		else if(len1==len2)
		{
			for(i=len1-1;i>=0;i--)
			{
				if(x[i]==y[i]) continue;
				else if(x[i]>y[i])
				{
					sub(x,y,len1);
					break;
				}
				else if(x[i]<y[i])
				{
					printf("-");
					sub(y,x,len1);
					break;
				}
			}
		    if(i==-1) sub(x,y,len1);
		}
	}
	return 0;
 } 

#include <cstdio>
#include <cstring>
#include <string>
#include <iostream>
#include <cmath>
#include <algorithm>
using namespace std;
int main()
{
	char chr1[100],chr2[100];
	int a[100]={0},b[100]={0},c[100]={0};
	int len1,len2,len;
	while(scanf("%s %s",chr1,chr2))
	{
		int i,j=0,k=0;
		len1=strlen(chr1);
		len2=strlen(chr2);
		for(i=len1-1;i>=0;i--) 
		{
			a[j]=chr1[i]-‘0‘;
			j++;
		}
		for(i=len2-1;i>=0;i--)
		{
			b[k]=chr2[i]-‘0‘;
			k++;
		}
		if(len1>len2) len=len1;
		else len=len2;
		int m=0;
		for(i=0;i<len;i++)
		{
			c[i]=(a[i]+b[i]+m)%10;
			if(a[i]+b[i]+m>=10) m=1;
			else m=0;
		}
		if(a[i-1]+b[i-1]+m>10) c[i]=1;
		else i=i-1;
		for(;i>=0;i--) cout<<c[i];
		cout<<endl;
	}
	return 0;
 }