目标需求：
//描述:
//长数相乘
//请编程实现：两个任意长度的数相乘，请输出结果.
//详细要求以及系统约束
//1）两个数可能是小数、整数、正数、负数；
//2）输入输出均为字符串形式，输入的字符串以“ ”结束，输出的结果字符串也必须以“ ”结束；
//3）输入的字符串不能是空字符串或非法字符串，否则返回-1，其他情况返回0；
//4）输出的结果字符串需要过滤掉整数位前以及小数位后无效的0，小数位为全0的，直接输出整数位；
//例1：相乘结果为11.345，此数值前后均不可以带0，“011.345”或者“0011.34500”等等前后带无效0的均视为错误输出。
//例2：080 × 0.125 结果是“10”
//5）输出的结果如果是正数或0需要过滤掉前面的+号。
//例1：相乘结果为+121，则“+121”为错误输出，“121”为正确输出。
//输入:
//输入两个任意长度的数
//输出:
//输出相乘的结果,如果输入的数不规范，输出结果为空
//样例输入:
//100000
//500000
//样例输出:
//50000000000
思路：
首先实现字符串加法，去除乘数以及被乘数的小数点，计算结果小数点位置，被乘数逐位与乘数相乘并进行相对的左移位(乘10)，然后对这些逐位相乘结果进行相加即可。
得到结果再进行截头截尾(去除结果字符串的开始的0串和小数末尾的0串)。
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
void str_z(char* s1, char* s2, char **s1z, char **s2z, int *sign){
int s1sign=1,s2sign=1;
if(s1[0]=='-'){
s1sign=-1;
*s1z = &s1[1];
}
else
*s1z = s1;
if(s2[0]=='-'){
s2sign=-1;
*s2z = &s2[1];
}
else
*s2z = s2;
*sign = s1sign*s2sign;
}
void zheng_xiao_fenli(char *s1, char* s2, int *xiaoshu_cnt, char **s1_num, char **s2_num){
int s1len, s2len;
int k1, k2, s1_xiaoshu_cnt=0, s2_xiaoshu_cnt=0;
s1len = strlen(s1);
s2len = strlen(s2);
for(k1=s1len-1; k1>=0; k1--){
if(s1[k1]>='0'&&s1[k1]<='9')
continue;
else if(s1[k1]=='.')
s1_xiaoshu_cnt += s1len-k1-1;
else{
exit(0); //非法字符
}
}
if(s1_xiaoshu_cnt==0){
*s1_num = s1;
}
else{
*s1_num = (char*)malloc(sizeof(char)*s1len);
/*if(*s1_num==NULL){
printf("malloc failed!
");
exit(0);
}*/
memcpy(*s1_num, s1, sizeof(char)*(s1len-s1_xiaoshu_cnt-1));
memcpy(*s1_num+s1len-s1_xiaoshu_cnt-1, s1+s1len-s1_xiaoshu_cnt, sizeof(char)*s1_xiaoshu_cnt);
*(*s1_num+s1len-1) = ' ';
}
for(k2=s2len-1; k2>=0; k2--){
if(s2[k2]>='0'&&s2[k2]<='9')
continue;
else if(s2[k2]=='.')
s2_xiaoshu_cnt += s2len-k2-1;
else{
exit(0); //非法字符
}
}
if(s2_xiaoshu_cnt==0){
*s2_num = s2;
}
else{
*s2_num = (char*)malloc(sizeof(char)*s2len);
/*if(*s2_num==NULL){
printf("malloc failed!
");
exit(0);
}*/
memcpy(*s2_num, s2, sizeof(char)*(s2len-s2_xiaoshu_cnt-1));
memcpy(*s2_num+s2len-s2_xiaoshu_cnt-1, s2+s2len-s2_xiaoshu_cnt, sizeof(char)*s2_xiaoshu_cnt);
*(*s2_num+s2len-1) = ' ';
}
*xiaoshu_cnt = s1_xiaoshu_cnt+s2_xiaoshu_cnt;
}
char* str_add(char* s1, char* s2){
int s1len,s2len,anslen;
int k1,k2,ansk,c,s;
char *ans,*ansrtn;
s1len=strlen(s1);
s2len=strlen(s2);
anslen=s1len>s2len?s1len+1:s2len+1;
ans = (char*)malloc(sizeof(char)*(anslen+1));
/*if(ans==NULL){
printf("malloc failed!
");
exit(0);
}*/
k1 = s1len-1;
k2 = s2len-1;
ansk = anslen-1;
s=0; c=0;
while(k1>=0||k2>=0){
if(k1>=0&&k2>=0){
c = s1[k1--]+s2[k2--]-'0'-'0'+s;
ans[ansk--] = c%10+'0';
s = c/10;
}
else if(k1>=0){
c = s1[k1--]-'0'+s;
ans[ansk--] = c%10+'0';
s = c/10;
}
else if(k2>=0){
c = s2[k2--]-'0'+s;
ans[ansk--] = c%10+'0';
s = c/10;
}
}
ans[0] = s+'0';
ans[anslen] = ' ';
for(ansk=0; ansk<anslen; ansk++){
if(ans[ansk]!='0')
break;
}
if(ansk!=0){
ansrtn = (char*)malloc(sizeof(char)*(anslen-ansk+1));
if(ansrtn==NULL){
printf("malloc failed!
");
exit(0);
}
strcpy(ansrtn, &ans[ansk]);
free(ans);
return ansrtn;
}
else
return ans;
}
char* str_mul(char* s1, char* s2){
int s1len, s2len, k1, k2, k;
char* mul_temp, *temp, *del_temp;
int mul_temp_len;
char* add_temp;
s1len = strlen(s1);
s2len = strlen(s2);
add_temp = (char*)malloc(sizeof(char)*2);
/*if(add_temp==NULL){
printf("malloc failed!
");
exit(0);
}*/
add_temp[0] = '0'; add_temp[1] = ' ';
for(k1=0; k1<s1len; k1++){
mul_temp = (char*)malloc(sizeof(char)*2);
/*if(mul_temp==NULL){
printf("malloc failed!
");
exit(0);
}*/
mul_temp[0] = '0'; mul_temp[1] = ' ';
if(s1[k1]=='0')
continue;
for(k=s1[k1]-'0'; k>0; k--){
del_temp = mul_temp;
mul_temp = str_add(mul_temp, s2);
free(del_temp);
}
mul_temp_len = strlen(mul_temp);
temp = (char*)malloc(sizeof(char)*(mul_temp_len+s1len-k1));
/*if(temp==NULL){
printf("malloc failed!
");
exit(0);
}*/
memset(temp, '0', sizeof(char)*(mul_temp_len+s1len-k1));
memcpy(temp, mul_temp, sizeof(char)*mul_temp_len);
temp[mul_temp_len+s1len-k1-1] = ' ';
free(mul_temp);
mul_temp = temp;
add_temp = str_add(mul_temp, add_temp);
}
//printf("%s", add_temp);
return add_temp;
}
int main(void){
char s1[100];
char s2[100];
int sign, xs_cnt, k, kk, kp;
char *s1z, *s2z;
char *s1zheng, *s1xiao, *s2zheng, *s2xiao, *s1_num, *s2_num;
char *ans; int anslen, xs_cnt_temp;
gets(s1);
gets(s2);
str_z(s1, s2, &s1z, &s2z, &sign);
zheng_xiao_fenli(s1z, s2z, &xs_cnt, &s1_num, &s2_num);
ans = str_mul(s1_num, s2_num);
anslen = strlen(ans);
printf("
");
if(sign==-1)
printf("-");
if(xs_cnt==0){
printf("%s", ans);
}
else{
if(anslen<=xs_cnt){
for(k=anslen-1; k>=0; k--){
if(ans[k]!='0')
break;
}
printf("0.");
xs_cnt_temp = xs_cnt-anslen;
while(xs_cnt_temp--){
printf("0");
}
for(kk=0; kk<=k; kk++){
printf("%c", ans[kk]);
}
}
else{
for(k=0; k<anslen-xs_cnt; k++){
printf("%c", ans[k]);
}
for(kk=anslen-1; kk>=k; kk--){
if(ans[kk]!='0')
break;
}
if(kk!=k-1){
printf(".");
for(kp=k; kp<=kk; kp++){
printf("%c", ans[kp]);
}
}
}
}
system("pause");
return 0;
}结果演示：
