大数减法


#include <iostream>

#include <cstring>

#include <cstdio>

using namespace std;

int max(int m,int n)

{

if(m>n)

return m;

return n;

}

int compare(char *str_a,char *str_b)

{

int len_a, len_b;

len_a = strlen(str_a); //分别获取大数的位数进行比较

len_b = strlen(str_b);

if ( strcmp(str_a, str_b) == 0 ) //返回比较结果

return 0;

if ( len_a > len_b )

return 1;

else if( len_a == len_b )

return strcmp(str_a, str_b);

else

return -1;

}

int main()

{

int f, n;

int i, k;

char str_a[1000], str_b[1000];

int num_a[1000] ; //初始化大数数组，各位全清0

int num_b[1000] ;

int num_c[1000];

while (scanf("%s%s",str_a,str_b)!= EOF) //可进行多组测试

{

memset(num_a,0,sizeof(num_a));

memset(num_b,0,sizeof(num_b));

int len_a = strlen(str_a); //分别获得两个大数的位数

int len_b = strlen(str_b);

k = max(len_a,len_b) ; //获得最大的位数;

num_c[0] = 0;

f = 0;

n = compare(str_a,str_b);

for (i=0;i<len_a;i++) //颠倒存储

num_a[i] = str_a[len_a-i-1] - '0';

for (i=0;i<len_b;i++)

num_b[i] = str_b[len_b-i-1] - '0';

for (i=0;i<k;i++) //逐位进行减法

{

if (n>=0)

{

if (num_a[i] >= num_b[i])

num_c[i] = num_a[i] - num_b[i];

else

{

num_c[i] = num_a[i] - num_b[i] + 10;

num_a[i+1]--;

}

}

else

{

if ( num_b[i] >= num_a[i])

num_c[i] = num_b[i] - num_a[i];

else

{

num_c[i] = num_b[i] - num_a[i] + 10;

num_b[i+1]--;

}

}

}

if (n<0) //按要求打印

printf("-");

for (i=k-1; i>=0; i--)

{

if (num_c[i])

f = 1;

if (f || i == 0 )

printf("%d",num_c[i]);

}

printf("\n");

}

return 0;

}