一元多项式简单计算器

发布网友 发布时间：2022-05-03 02:13

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热心网友 时间：2022-07-01 12:31

#include <iostream>
#include <cstdlib>
#include <cctype>
using namespace std;

void eatspaces(char* str);
double expr(char* str);
double term(char* str,int& index);
double number(char* str,int& index);
char* extract(char* str, int& index);

const int MAX = 80;

int main()
{
char buffer[MAX] = {0};
cout<< endl
<< "欢迎使用计算器"<<endl
<<"请输入表达式进行计算或者输入空白行退出"<<endl;
for(;;)
{
cin.getline(buffer,sizeof buffer);
eatspaces(buffer);

if(!buffer[0])
return 0;

cout<<"\t="<<expr(buffer)
<<endl<<endl;
}
}

void eatspaces(char* str)
{
int i = 0;
int j = 0;

while((*(str + i)= *(str + j++)) !='\0')
if(*(str + i) != ' ')
i++;
return;
}

double expr(char* str)
{
double value = 0.0;
int index = 0;

value = term(str,index);

for(;;)
{
switch(*(str + index++))
{
case '\0':
return value;

case '+':
value += term(str,index);
break;

case '-':
value -= term(str,index);
break;

default:
cout<<endl
<<"输入错误"
<<endl;
exit(1);
}
}
}

double term(char* str, int& index)
{
double value = 0.0;

value = number(str, index);

while((*(str + index) == '*')||(*(str + index) == '/'))
{
if(*(str + index) == '*')
value *= number(str, ++index);
if(*(str + index) == '/')
value /= number(str,++index);
}
return value;
}

double number(char* str,int& index)
{
double value = 0.0;

if(*(str + index) == '(')
{
char* psubstr = 0;
psubstr = extract(str,++index);
value = expr(psubstr);
delete[]psubstr;
return value;
}

while(isdigit(*(str + index)))
value = 10*value + (*(str + index++) - 48);

if(*(str + index)!= '.')
return value;

double factor = 1.0;
while(isdigit(*(str + (++index))))
{
factor = value + (*(str + index) - 48)*factor;
}

return value;
}

char* extract(char* str, int& index)
{
char buffer[MAX];
char* pstr = 0;
int numL = 0;
int bufindex = index;

do
{
buffer[index - bufindex] = *(str + index);
switch(buffer[index - bufindex])
{
case ')':
if(numL == 0)
{
buffer[index - bufindex] = '\0';
++index;
pstr = new char[index - bufindex];
if(!pstr)
{
cout<<"输入错误"<<endl;
exit(1);
}
strcpy_s(pstr,index-bufindex,buffer);
return pstr;
}
else
numL--;
break;
case '(':
numL++;

break;
}
}while(*(str + index++) != '\0');

cout<<"输入错误"<<endl;
exit(1);
return pstr;
}

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本人也是学生，不是高手,大家共同学习，共同进步。回答可能不是完全正确，希望原谅。