数据结构课程设计 算术表达式求值

//Evaluate Expression

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

int A[7][7] = {3,3,2,2,2,3,3,
3,3,2,2,2,3,3,
3,3,3,3,2,3,3,
3,3,3,3,2,3,3,
2,2,2,2,2,1,0,
3,3,3,3,0,3,3,
2,2,2,2,2,0,1}; //存放运算符的优先顺序，3为>,2为<,1为＝

bool isoperator(char optr)  //判断是否操作符
{
switch(optr)
{
case '+':
case '-':
case '*':
case '/':
case '(':
case ')':
case '#':return true;
default:return false;
}
}

int crd(char c)     //寻找字符所在的行列坐标
{
switch(c)
{
case'+': return 0;
case'-': return 1;
case'*': return 2;
case'/': return 3;
case'(': return 4;
case')': return 5;
case'#': return 6;
}
}

char preced(char a, char b) //判断运算符的优先关系
{
int m, n;
m = crd(a);
n = crd(b);
switch(A[m]
)
{
case 3:return '>';
case 2:return '<';
case 1:return '=';
}
}

int push_opnd(double *&opnd, char *&expr, int top_opnd, int i)  //操作数压栈
{
int j;
double suma = 0.0, sumb = 0.0;
double e = 0.1, tmp;

for(j = i; isdigit(expr[j]); j++)
{
tmp = expr[j] - '0';
suma = suma * 10 + tmp;
}
if(expr[j] == '.')
{
for(j++; isdigit(expr[j]); j++)
{
sumb += (expr[j] - '0') * e;
e /= 10;
}
}
opnd[top_opnd] = suma + sumb;
return j;
}

void operate(double *&opnd, char *&optr, int top_opnd, int top_optr)
{ //计算并把结果压栈
switch(optr[top_optr - 1])
{
case '+': opnd[top_opnd - 2] += opnd[top_opnd - 1];break;
case '-': opnd[top_opnd - 2] -= opnd[top_opnd - 1];break;
case '*': opnd[top_opnd - 2] *= opnd[top_opnd - 1];break;
case '/': if(opnd[top_opnd - 1] == 0)
{
cout << "Error! The divisor is 0" << endl;
system("pause");
exit(1);
}
opnd[top_opnd - 2] /= opnd[top_opnd - 1];
break;
}
}

int main()
{
double *OPND;	//运算数栈
char *OPTR;		//运算符栈
char *EXPR;		//表达式
char str[100];

int top_opnd = 0;	//运算数栈顶计数器
int top_optr = 0;	//运算符栈顶计数器
int len;		//表达式长度
int i;      //下标

cout << "Input the EXPRession: ";
cin >> str;
len = strlen(str);

EXPR = new char[len + 3];
OPND = new double[len];
OPTR = new char[len];

//在表达式前后加上'#'
EXPR[0] = '#';
for(i = 0; str[i] != '\0'; i++)
EXPR[i + 1] = str[i];
EXPR[len + 1] = '#';
EXPR[len + 2] = '\0';

//cout << EXPR << endl;
OPTR[top_optr++] = '#';
i = 1;
while(EXPR[i] != '#' || OPTR[top_optr - 1] != '#')
{
if(isdigit(EXPR[i]))
{
i = push_opnd(OPND, EXPR, top_opnd, i);
top_opnd++;
}
else if(isoperator(EXPR[i]))
{
switch(preced(OPTR[top_optr - 1], EXPR[i]))
{
case '<': OPTR[top_optr++] = EXPR[i];
i++;
break;
case '=': top_optr--;
i++;
break;
case '>': operate(OPND, OPTR, top_opnd, top_optr);
top_opnd--;
top_optr--;
break;
}
}
}

cout << OPND[0] << endl;

delete EXPR;
delete OPND;
delete OPTR;

system("pause");
return 0;
}