河南美孚机油总代理:科学计算器如何用C程序……

#include <iostream.h>
#include <string>
using namespace std;

/**************Simple Calculator Code*************************
This program is abstracted from <C++ Programming Language>
all the ideas belong to original author

you can study from it

how to use ?
input a line of expression which is ended with ";"
Examples:
you put :
3+(5+6)*(-1+8);
the reult :
80
and you can continue ...
***********************************************************/
enum Token_value{
NAME, NUMBER, END,
PLUS = '+', MINUS = '-',MUL = '*',DIV = '/',
PRINT = ';',ASSIGN = '=',LP = '(',RP = ')'
};

Token_value curr_tok = PRINT;

// fuction list//////////////////////////////////////
double expr(bool get);
double term(bool get);
double prim(bool get);
Token_value get_token();
double error(const string &s);

//////////////////////////////////////////////////////////
double expr(bool get) //plus and minus
{
double left = term(get);
for(;;)
{
switch(curr_tok){
case PLUS:
left+=term(true);
break;
case MINUS:
left-=term(true);
break;
default:
return left;
}
}
}

double term(bool get) // multiply and divide
{
double left = prim(get);
for(;;)
{
switch(curr_tok){
case MUL:
left*=prim(true);
break;
case DIV:
if(double d = prim(true)){ // no zero!!
left/= d;
break;
}
return error("divide by zero!!\n");
default :
return left;
}
}
}

double number_value;
double string_value;

double prim(bool get)
{
if(get) get_token();

switch(curr_tok){
case NUMBER:
{
double v = number_value;
get_token();
return v;
}
case NAME:
{
double v;
//double &v = table[string_value];
//this table reserved the name mapped with variable
//now we don't use it!
if(get_token()==ASSIGN)
v = expr(true);
return v;
}
case MINUS: // negative
{
return -prim(true);
}
case LP:
{
double e = expr(true);
if(curr_tok!=RP)return error(")expected");
get_token(); // absorb )
return e;
}
default:
return error("primary expected"); // no primary
}
}

Token_value get_token()
{
char ch =0;
cin>>ch;
switch(ch){
case 0:
return curr_tok=END; //return and assignment
case ';':
case '*':
case '/':
case '+':
case '-':
case '(':
case ')':
case '=':
return curr_tok = Token_value(ch);
case '0':case '1':case '2':case '3':case '4':
case '5':case '6':case '7':case '8':case '9':
case '.':
cin.putback(ch);
cin>>number_value;
return curr_tok = NUMBER;
default:
if(isalpha(ch))
{
cin.putback(ch);
cin>>string_value;
return curr_tok = NAME;
}
error("bad token!");
return curr_tok = PRINT;
}
}

int no_of_error;

double error(const string &s)
{
no_of_error++;
cout<<"error:"<<s.data()<<"\n";
return 1;
}

int main()
{
while(cin)
{
get_token();
if(curr_tok==END)break;
if(curr_tok==PRINT) continue;
cout<<expr(false)<<'\n';
}

return no_of_error;
}
不知道为什么，在VC下的汉字在这里是乱码，没办法，程序里我只能用English
程序的主要思想：
利用自顶向下的分析方法:(编译原理）
E= E(+|-)T
T =T(*|/)P
P = i|(E)
不用定义太复杂的数据结构，我是从Bjarne Stroustrup那本书上的代码稍做修改写的这个，给你一个参考。

就这么给你讲你也不晓得！还是自己买一本书看看！就晓得怎么编程啦！
只是给你一点建议！

#include <stdio.h>
#include <string.h>
struct list
{
int index;
int a;
char b;
};
struct list s[100];
/*进堆比较*/
int comp1(char a,char b)
{
char op[4][2]={'*','/','+','-','(','(',')',')'};
int i;
int a1,b1;
for(i=0;i<4;i++)
if (a==op[i][0] || a==op[i][1])
{
a1=i;
break;
}
for(i=0;i<4;i++)
if (b==op[i][0] || b==op[i][1])
{
b1=i;
break;
}
if (a1<b1) return 1;
else return 0;
}
int comp2(char a,char b)
{
char op[4][2]={'(','(','*','/','+','-',')',')'};
int i;
int a1,b1;
for(i=0;i<4;i++)
if (a==op[i][0] || a==op[i][1])
{
a1=i;
break;
}
for(i=0;i<4;i++)
if (b==op[i][0] || b==op[i][1])
{
b1=i;
break;
}
if (a1<b1) return 1;
else return 0;
}
int oper(int a,int b,char op)
{
int result;
if(op=='*') result=a*b;
else if(op=='/') result=a/b;
else if(op=='+') result=a+b;
else if(op=='-') result=a-b;
return result;
}

int main()
{
int len=0,i=0,j;
int m,n,result;
char op;
int number=0;
char enter[100];
int s1[100],top1=0,top2=0;
char s2[100];
s2[top2]='(';top2++;
scanf("%s",enter);
for(i=0;i<strlen(enter);i++)
{
if(enter[i]>='0' && enter[i]<='9')
{
if (enter[i+1]>='0' && enter[i+1]<='9')
number=10*number+enter[i]-'0';
else
{
s[len].index=1;
s[len].a=10*number+enter[i]-'0';
s[len].b='0';
len++;
number=0;
}
}
else
{

s[len].index=0;
s[len].a=0;
s[len].b=enter[i];
len++;
}
/*printf("len@=%d,i=%d\n",len,i); */
}
if (enter[strlen(enter)-1]!='=')
{
s[len].index=0;
s[len].a=0;
s[len].b='=';
len++;
}
/*for (i=0;i<len;i++)
{
if (s[i].index)
cout<<s[i].index<<" "<<s[i].a<<endl;
else
cout<<s[i].index<<" "<<s[i].b<<endl;
}*/
/*printf("len=%d\n",len); */
for(i=0;i<len;i++)
{
if (s[i].b=='=')
{
while(top1!=1)
{
m=s1[top1-1];
top1--;
n=s1[top1-1];
top1--;
op=s2[top2-1];
top2--;
result=oper(n,m,op);
s1[top1]=result;
top1++;
}
printf("%d\n",s1[top1-1]);
break;
}
if (s[i].b==')')
{
while(s2[top2-1]!='(')
{
m=s1[top1-1];
top1--;
n=s1[top1-1];
top1--;
op=s2[top2-1];
top2--;
result=oper(n,m,op);
s1[top1]=result;
top1++;
}
top2--;
}
else
{
if(s[i].index==1)
{
s1[top1]=s[i].a;
top1++;
}
else
{
if (comp1(s[i].b,s2[top2-1])==1)
{
s2[top2]=s[i].b;
top2++;
}
else
{
if(comp2(s[i].b,s2[top2-1])==0)
{
m=s1[top1-1];
top1--;
n=s1[top1-1];
top1--;
op=s2[top2-1];
top2--;
result=oper(n,m,op);
s1[top1]=result;
top1++;
}
s2[top2]=s[i].b;
top2++;
}
}
}
/*
if (s[i].index==1)
{
for (j=0;j<top1;j++)
printf("%d ",s1[j]);
printf("\n");
}
if (s[i].index==0)
{
for (j=0;j<top2;j++)
printf("%c ",s2[j]);
printf("\n");
}
*/
}
/*cout<<s1[0]<<endl; */
/*char a,b;
while(cin>>a>>b)
{
cout<<comp1(a,b)<<" "<<comp2(a,b)<<endl;
}
*/
getch();
}

可以求比如:
12+2+3
2*21*3+4/2
14*(22+12)-2

//最好去看看数据结构的书,里面有讲
//这是我用C++写的,很不完善.