计算器
//
// This is example code from Chapter 6.7 "Trying the second version" of
// "Programming -- Principles and Practice Using C++" by Bjarne Stroustrup
//
#include "std_lib_facilities.h"
//------------------------------------------
class Token {
public:
char kind; // what kind of token
double value; // for numbers: a value
Token(char ch) // make a Token from a char
:kind(ch), value(0) { }
Token(char ch, double val) // make a Token from a char and a double
:kind(ch), value(val) { }
};
//------------------------------------------
class Token_stream {
public:
Token_stream(); // make a Token_stream that reads from cin
Token get(); // get a Token (get() is defined elsewhere)
void putback(Token t); // put a Token back
private:
bool full; // is there a Token in the buffer?
Token buffer; // here is where we keep a Token put back using putback()
};
//------------------------------------------
// The constructor just sets full to indicate that the buffer is empty:
Token_stream::Token_stream()
:full(false), buffer(0) // no Token in buffer
{
}
//------------------------------------------
// The putback() member function puts its argument back into the Token_stream's buffer:
void Token_stream::putback(Token t)
{
if (full) error("putback() into a full buffer");
buffer = t; // copy t to buffer
full = true; // buffer is now full
}
//------------------------------------------
Token Token_stream::get()
{
if (full) { // do we already have a Token ready?
// remove token from buffer
full=false;
return buffer;
}
char ch;
cin >> ch; // note that >> skips whitespace (space, newline, tab, etc.)
switch (ch) {
case ';': // for "print"
case 'q': // for "quit"
case '(': case ')': case '+': case '-': case '*': case '/':
return Token(ch); // let each character represent itself
case '.':
case '0': case '1': case '2': case '3': case '4':
case '5': case '6': case '7': case '8': case '9':
{
cin.putback(ch); // put digit back into the input stream
double val;
cin >> val; // read a floating-point number
return Token('8',val); // let '8' represent "a number"
}
default:
error("Bad token");
}
}
//------------------------------------------
Token_stream ts; // provides get() and putback()
//------------------------------------------
double expression(); // declaration so that primary() can call expression()
//------------------------------------------
// deal with numbers and parentheses
double primary()
{
Token t = ts.get();
switch (t.kind) {
case '(': // handle '(' expression ')'
{
double d = expression();
t = ts.get();
if (t.kind != ')') error("')' expected");
return d;
}
case '8': // we use '8' to represent a number
return t.value; // return the number's value
default:
error("primary expected");
}
}
//------------------------------------------
// deal with *, /, and %
double term()
{
double left = primary();
Token t = ts.get(); // get the next token from token stream
while(true) {
switch (t.kind) {
case '*':
left *= primary();
t = ts.get();
break;
case '/':
{
double d = primary();
if (d == 0) error("divide by zero");
left /= d;
t = ts.get();
break;
}
default:
ts.putback(t); // put t back into the token stream
return left;
}
}
}
//------------------------------------------
// deal with + and -
double expression()
{
double left = term(); // read and evaluate a Term
Token t = ts.get(); // get the next token from token stream
while(true) {
switch(t.kind) {
case '+':
left += term(); // evaluate Term and add
t = ts.get();
break;
case '-':
left -= term(); // evaluate Term and subtract
t = ts.get();
break;
default:
ts.putback(t); // put t back into the token stream
return left; // finally: no more + or -: return the answer
}
}
}
//------------------------------------------
int main()
{try
{
double val = 0;
while (cin) {
Token t = ts.get();
if (t.kind == 'q') break; // 'q' for quit
if (t.kind == ';') // ';' for "print now"
cout << "=" << val << '\n';
else
ts.putback(t);
val = expression();
}
}
catch (exception& e) {
cerr << "error: " << e.what() << '\n';
return 1;
}
catch (...) {
cerr << "Oops: unknown exception!\n";
return 2;
}}
//------------------------------------------
int main中while(cin)怎么解释
[解决办法]
while(cin)
流必须处于无错误状态，才能用入输入输出，当希望输入数值型数据时输入了字符，流会处于错误状态，或者到文件结束符时也会置cin为false;
[解决办法]
可以这么理解：while(bool){}while 的用法是如果括号里面的条件为真的话就执行{}里面的内容，如果满足条件就执行、这样可以不断的循环执行、
while的中断
1.(bool)为false
2.{}中定义break;这种最常用，
这句while（cin）{} 相当于while(1){}，必然成立的、cin会不断的执行，直到满足条件的break发生才会中断
3、其实for和while 在某些情况下是可以对等的、区别是for()要定义循环次数，但是while不必给定循环次数、
比如while(int x<500)就跟for()就差不多、但是while(cin)这种循环机制在for()里面实现可就不一样了、
------解决方案--------------------
/*---------------------------------------函数型计算器(VC++6.0,Win32 Console)程序由 yu_hua 于2007-07-27设计完成功能：目前提供了10多个常用数学函数: ⑴正弦sin ⑵余弦cos ⑶正切tan ⑷开平方sqrt ⑸反正弦arcsin ⑹反余弦arccos ⑺反正切arctan ⑻常用对数lg ⑼自然对数ln ⑽ｅ指数exp ⑾乘幂函数∧用法：如果要求2的32次幂，可以打入2^32<回车>如果要求30度角的正切可键入tan(Pi/6)<回车>注意不能打入：tan(30)<Enter>如果要求1.23弧度的正弦，有几种方法都有效：sin(1.23)<Enter>sin 1.23 <Enter>sin1.23 <Enter>如果验证正余弦的平方和公式,可打入sin(1.23)^2+cos(1.23)^2 <Enter>或sin1.23^2+cos1.23^2 <Enter>此外两函数表达式连在一起,自动理解为相乘如：sin1.23cos0.77+cos1.23sin0.77就等价于sin(1.23)*cos(0.77)+cos(1.23)*sin(0.77)当然你还可以依据三角变换，再用sin(1.23+0.77)也即sin2验证一下。本计算器充分考虑了运算符的优先级因此诸如：2+3*4^2 实际上相当于：2+(3*(4*4))另外函数名前面如果是数字,那么自动认为二者相乘.同理，如果某数的右侧是左括号，则自动认为该数与括弧项之间隐含一乘号。如：3sin1.2^2+5cos2.1^2 相当于3*sin2(1.2)+5*cos2(2.1)又如：4(3-2(sqrt5-1)+ln2)+lg5 相当于4*(3-2*(√5 -1)+loge(2))+log10(5)此外，本计算器提供了圆周率 Pi键入字母时不区分大小写,以方便使用。----------------------------------------*/#include <iostream>#include <iomanip>#include <cstdlib>#include <cstring>#include <cctype>#include <cmath>#include <stdio.h>#include <string.h>#include <windows.h>using namespace std;const char Tab=0x9;const int DIGIT=1;const int MAXLEN=16384;char s[MAXLEN],*endss;int pcs=15;double fun(double x,char op[],int *iop) { while (op[*iop-1]<32) //本行使得函数嵌套调用时不必加括号,如 arc sin(sin(1.234)) 只需键入arc sin sin 1.234<Enter> switch (op[*iop-1]) { case 7: x=sin(x); (*iop)--;break; case 8: x=cos(x); (*iop)--;break; case 9: x=tan(x); (*iop)--;break; case 10: x=sqrt(x); (*iop)--;break; case 11: x=asin(x); (*iop)--;break; case 12: x=acos(x); (*iop)--;break; case 13: x=atan(x); (*iop)--;break; case 14: x=log10(x);(*iop)--;break; case 15: x=log(x); (*iop)--;break; case 16: x=exp(x); (*iop)--;break; } return x;}double calc(char *expr,char **addr) { static deep; //递归深度 static char *fname[]={ "sin","cos","tan","sqrt","arcsin","arccos","arctan","lg","ln","exp",NULL}; double ST[10]={0.0}; //数字栈 char op[10]={'+'}; //运算符栈 char c,*rexp,*pp,*pf; int ist=1,iop=1,last; if (!deep) { pp=pf=expr; do { c = *pp++; if (c!=' '&& c!=Tab) *pf++ = c; } while (c!='\0'); } pp=expr; if ((c=*pp)=='-'||c=='+') { op[0] = c; pp++; } last = !DIGIT; while ((c=*pp)!='\0') { if (c=='(') {//左圆括弧 deep++; ST[ist++]=calc(++pp,addr); deep--; ST[ist-1]=fun(ST[ist-1],op,&iop); pp = *addr; last = DIGIT; if (*pp == '('||isalpha(*pp) && strnicmp(pp,"Pi",2)) {//目的是：当右圆括弧的右恻为左圆括弧或函数名字时，默认其为乘法 op[iop++]='*'; last = !DIGIT; c = op[--iop]; goto operate ; } } else if (c==')') {//右圆括弧 pp++; break; } else if (isalpha(c)) { if (!strnicmp(pp,"Pi",2)) { if (last==DIGIT) { cout<< "π左侧遇）" <<endl;exit(1); } ST[ist++]=3.14159265358979323846264338328; ST[ist-1]=fun(ST[ist-1],op,&iop); pp += 2; last = DIGIT; if (!strnicmp(pp,"Pi",2)) { cout<< "两个π相连" <<endl;exit(2); } if (*pp=='(') { cout<< "π右侧遇（" <<endl;exit(3); } } else { for(int i=0; (pf=fname[i])!=NULL; i++) if (!strnicmp(pp,pf,strlen(pf)))break; if (pf!=NULL) { op[iop++] = 07+i; pp += strlen(pf); } else { cout<< "陌生函数名" <<endl;exit(4); } } } else if (c=='+'||c=='-'||c=='*'||c=='/'||c=='^') { char cc; if (last != DIGIT) { cout<< "运算符粘连" <<endl;exit(5); } pp++; if (c=='+'||c=='-') { do { cc = op[--iop]; --ist; switch (cc) { case '+': ST[ist-1] += ST[ist];break; case '-': ST[ist-1] -= ST[ist];break; case '*': ST[ist-1] *= ST[ist];break; case '/': ST[ist-1] /= ST[ist];break; case '^': ST[ist-1] = pow(ST[ist-1],ST[ist]);break; } } while (iop); op[iop++] = c; } else if (c=='*'||c=='/') {operate: cc = op[iop-1]; if (cc=='+'||cc=='-') { op[iop++] = c; } else { --ist; op[iop-1] = c; switch (cc) { case '*': ST[ist-1] *= ST[ist];break; case '/': ST[ist-1] /= ST[ist];break; case '^': ST[ist-1] = pow(ST[ist-1],ST[ist]);break; } } } else { cc = op[iop-1]; if (cc=='^') { cout<< "乘幂符连用" <<endl;exit(6); } op[iop++] = c; } last = !DIGIT; } else { if (last == DIGIT) { cout<< "两数字粘连" <<endl;exit(7); } ST[ist++]=strtod(pp,&rexp); ST[ist-1]=fun(ST[ist-1],op,&iop); if (pp == rexp) { cout<< "非法字符" <<endl;exit(8); } pp = rexp; last = DIGIT; if (*pp == '('||isalpha(*pp)) { op[iop++]='*'; last = !DIGIT; c = op[--iop]; goto operate ; } } } *addr=pp; if (iop>=ist) { cout<< "表达式有误" <<endl;exit(9); } while (iop) { --ist; switch (op[--iop]) { case '+': ST[ist-1] += ST[ist];break; case '-': ST[ist-1] -= ST[ist];break; case '*': ST[ist-1] *= ST[ist];break; case '/': ST[ist-1] /= ST[ist];break; case '^': ST[ist-1] = pow(ST[ist-1],ST[ist]);break; } } return ST[0];}int main(int argc,char **argv) { if (argc<=1) { if (GetConsoleOutputCP()!=936) system("chcp 936>NUL");//中文代码页 cout << "计算函数表达式的值。"<<endl<<"支持(),+,-,*,/,^,Pi,sin,cos,tan,sqrt,arcsin,arccos,arctan,lg,ln,exp"<<endl; while (1) { cout << "请输入表达式："; gets(s); if (s[0]==0) break;// cout << s <<"="; cout << setprecision(15) << calc(s,&endss) << endl; } } else { strncpy(s,argv[1],MAXLEN-1);s[MAXLEN-1]=0; if (argc>=3) { pcs=atoi(argv[2]); if (pcs<0||15<pcs) pcs=15; printf("%.*lf\n",pcs,calc(s,&endss)); } else { printf("%.15lg\n",calc(s,&endss)); } } return 0;}