main.cpp

表达式求值,可以实现输入的任意表达式求值,包括含有括号.课程设计题目

#include <iostream.h>
#include <math.h>
#include <conio.h>
#include <string.h>
#include <stdlib.h>
const int maxstacksize = 50;
template <class t>
class stack
{ private:
	t stacklist[maxstacksize];int top;
public:
	stack (void):top(-1){}
	void push (const t& item);
	t pop (void);
	void clearstack(void){ top = -1;}
	t peek (void) const;
	int stackempty(void) const{ return top == -1;}
	int stackfull(void) const{ return top == maxstacksize-1;   }
};
template <class t>
void stack<t>::push (const t& item)
{    if (top == maxstacksize-1){cerr << "stack overflow!" << endl;exit(1); }
    top++;   stacklist[top] = item; }
template <class t>
t stack<t>::pop (void)
{  t temp;
    if(top == -1){cerr << "attempt to pop an empty stack!" << endl;exit(1); }
    temp = stacklist[top];   top--;   return temp;}

template <class t>
t stack<t>::peek (void) const
{if(top == -1){cerr << "attempt to peek at an empty stack!"<<endl;exit(1);}
 return stacklist[top];  }


class calculator
{private:
   stack<float> s;
   stack<char> optr;
   int  youxian(char a,char b);
 public:
 bool  gettwooperands(float& opnd1, float& opnd2);
 void compute(char op);
 float run(char *a);
};
int calculator:: youxian(char a,char b)
{if(b=='#'||b=='(')return 1;
 if (a=='+'||a=='-')return -1;
 if ((a=='*'||a=='/')&&(b=='-'||b=='+'))return 1;
 if ((a=='*'||a=='/')&&(b=='*'||b=='/'||b=='^'))return -1;
 if (a=='^'&&(b=='-'||b=='+'||b=='*'||b=='/'))return 1;
 if (a=='^'&&b=='^')return -1;
 return 0;
 }
bool calculator:: gettwooperands(float& opnd1, float& opnd2)
{if(s.stackempty()) { cerr << "missing operand!" << endl;return false;}
 opnd1 = s.pop();
 if(s.stackempty()){ cerr << "missing operand!" << endl;return false;}
 opnd2 = s.pop();
 return true;
}
void calculator::compute(char op)
{  bool result;  float operand1, operand2;
   result = gettwooperands(operand1, operand2);
   if (result == true)
    { switch(op)
	{case '+':   s.push(operand2+operand1);break;
	 case '-':   s.push(operand2-operand1);break;
	 case '*':   s.push(operand2*operand1);break;
	 case '/':   if (operand1 == 0)
			{ cerr << "divide by 0!" << endl;s.clearstack();}
		     else  s.push(operand2/operand1);break;
	case '^':   s.push(pow(operand2,operand1));break;
	}
    }
    else  s.clearstack();
}
float calculator::run(char *a)
{
s.clearstack();
optr.clearstack();
optr.push('#');
int i=0;
char c,op;
float x;
while (a[i]=='('){optr.push('(');i++;}
for(;i<strlen(a);)
{ if((a[i]>='0'&&a[i]<='9') ||a[i]=='-'||a[i]=='+')
  {x=atof(a+i);i++;
   while((a[i]>='0'&&a[i]<='9')||a[i]=='.')i++;
   s.push(x);
   c=a[i];
   if(c=='+'||c=='-'||c=='*'||c=='/'||c=='^')
     {i++;  while (youxian(c,optr.peek())<0) {op=optr.pop(); compute(op);}
	    if (youxian(c,optr.peek())>0){optr.push(c);}
      while (a[i]=='('){optr.push('(');i++;}
      if (!((a[i]>='0'&&a[i]<='9')||a[i]=='-'||a[i]=='+'))
	    {cout<<"error\n;" ;exit(0);}
     }
  }
 else if (a[i]==')')
     {while((op=optr.pop())!='('){compute(op);}
     i++; c=a[i];
     if(c=='+'||c=='-'||c=='*'||c=='/'||c=='^')
       {i++;  while (youxian(c,optr.peek())<0) {op=optr.pop(); compute(op);}
	if (youxian(c,optr.peek())>0){optr.push(c);}
	if (!((a[i]>='0'&&a[i]<='9')||a[i]=='-'||a[i]=='+'))
	    {cout<<"error shizi\n;" ;exit(0);}
       }
     }
 else {cout<<a[i]<<"error shizi\n";exit(0);}
}
while(optr.peek()!='#'){compute(optr.pop());}
return s.peek();
}

void main()
{
char ch;
char a[100];
do
{cout<<"放入一个只能含有小括号的算术表达式+-*/^:\n";
cin.getline(a,100,'\n');
calculator cal;
cout<<cal.run(a)<<'\0';
}while(ch);
}