两个大整数相乘程序

r囧r小猫 2022-08-12 12:59 215阅读 0赞

设计程序实现两个很大的数相乘，例如123456789\*987654321 。

#include <stdio.h>
    #include <string.h>
    #include <stdlib.h>
    
    void mux(const char *numA, const char *numB, char *result);
    char *reverse(const char *src, char *dst);
    void mux_ch_str(const char ch, const char *str, char *result);
    void add_str(char *dst, const char *src);
    
    int main(void)
    {
    	char numA[100] = "";
    	char numB[100] = "";
    	char *result = NULL;
    
    	printf("input numA = ");
    	fflush(stdout);
    	scanf("%s", numA);
    
    	printf("input numB = ");
    	fflush(stdout);
    	scanf("%s", numB);
    
    	result = (char *)malloc(strlen(numA) + strlen(numB) + 1);
    	mux(numA, numB, result);
    	printf("%s x %s = %s \n", numA, numB, result);
    
    	free(result);
    	result = NULL;
    	return 0;
    }
    
    /*字符串相乘, result = numA x numB, numA, numB顺序排列*/
    void mux(const char *numA, const char *numB, char *result)
    {
    	char *A = NULL;  //numA逆序串
    	char *B = NULL;  //numB逆序串
    	char *t = NULL;  //存储字符与字符串相乘结果
    	char *r = NULL;  //存储字符串与字符串相乘结果
    	int  i  = 0;
    
    	A = (char *)malloc(strlen(numA)+1);
    	B = (char *)malloc(strlen(numB)+1);
    	t = (char *)malloc(strlen(numA) + strlen(numB) + 1);
    	r = (char *)malloc(strlen(numA) + strlen(numB) + 1);
    
    	memset(A, 0, strlen(numA) + 1);
    	memset(B, 0, strlen(numB) + 1);
    	memset(t, 0, strlen(numA) + strlen(numB) + 1);
    	memset(r, 0, strlen(numA) + strlen(numB) + 1);
    
    	reverse(numA, A); //numA翻转保存为A
    	reverse(numB, B); //numB翻转保存为B
    
    	i = 0;
    	while (A[i])
    	{
    		memset(t, 0, strlen(numA) + strlen(numB) + 1);
    		mux_ch_str(A[i], B, t);  //从A串取下一个字符与B串相乘,结果保存在t串
    		add_str(r+i, t);   //将t串累加至result串
    		i++;
    	}
    
    	reverse(r, result);
    
    	free(A);
    	free(B);
    	free(t);
    	free(r);
    }
    
    /*字符串逆序排列 src -> dst*/
    char *reverse(const char *src, char *dst)
    {
    	int count = 0;
    	int i = 0;
    
    	while(src[count])
    	count++;
    	for (i=0; i<count; i++)
    	{
    		dst[i] = src[count - 1 - i];
    	}
    	dst[count] = '\0';
    	return dst;
    }
    
    /*字符乘字串,result = ch x str, str, result为逆序排列*/
    void mux_ch_str(const char ch, const char *str, char *result)
    {
    	char r = 0; //相乘结果
    	char c = 0; //进位数字
    	int i = 0;
    
    	while (str[i])
    	{
    		r = c + (ch - '0')*(str[i] - '0');
    		result[i] = r % 10 + '0';
    		c = r / 10;
    		i++;
    	}
    	if (c > 0)
    	{
    		result[i] = c + '0';
    		i++;
    	}
    	result[i] = '\0';
    }
    
    /*字符串相加,dst = dst + src, dst, src为逆序排列*/
    void add_str(char *dst, const char *src)
    {
    	char r = 0; //相加结果
    	char c = 0; //进位数字
    	int i = 0;
    
    	while(dst[i] || src[i])
    	{
    		r = c; 
    		if(dst[i])
    			r += dst[i] - '0';
    		if(src[i])
    			r += src[i] - '0';
    		dst[i] = r % 10 + '0';
    		c = r / 10;
    		i++;
    	}
    	if (c > 0)
    	{
    		dst[i] = c + '0';
    		i++;
    	}
    	dst[i] = '\0';
    }