#include <cstdio> #include <cstdlib> #include <cstring> class CalcInfixExp { public:    CalcInfixExp();    char calc(double &result, const char *s);    void error(char n);    char GetOrder(char a, char b);    bool NumPush(const char &a);    bool NumPop(char &a);    bool OpePush(const char &a);    bool OpePop(char &a); private:    int p, q;    char ope[100];    char num[100]; }; CalcInfixExp::CalcInfixExp() {    p=q=0; }; bool CalcInfixExp::NumPush(const char &a) {    if (q>=100) return false;    num[q++]=a;    return true; } char CalcInfixExp::calc(double &result, const char *s) {    bool PopRight;    char f, szA[20], order;    int i;    double a, b, c;    p=q=0; //清空ope栈和num栈    OpePush('\0');    if (*s=='+') s++;    else if (*s=='-')    {       s++;       OpePush('-');       NumPush('0');       NumPush(',');    }    do    {       if (*s>='0' && *s<='9' || *s=='。
  ')       {          do NumPush(*s++);          while (*s>='0' && *s<='9' || *s=='。');          NumPush(',');       }       else       {          OpePop(f);          switch (order=GetOrder(f, *s))          {          case '<':             OpePush(f);             OpePush(*s++);             if (*s=='+') s++;             else if (*s=='-')             {                s++;                OpePush('-');                NumPush('0');                NumPush(',');             }             break;          case '>':             //从num栈中获取第一个操作数             i=0;             if (q==0)             {                error('\4'); //num栈已空                return false;             }             NumPop(szA[i]);             do NumPop(szA[i]);             while (szA[i++]!=',');             szA[--i]='\0';             strrev(szA);             b=atof(szA);  //从num栈中获取第二个操作数             i=0;             if (q==0)             {                error('\4'); //num栈已空                return false;             }             do PopRight=NumPop(szA[i]);             while (szA[i++]!=',' && PopRight);             if (PopRight) NumPush(',');             szA[--i]='\0';             strrev(szA);             a=atof(szA);             //计算             switch (f)             {             case '+': c=a+b; break;             case '-': c=a-b; break;             case '*': c=a*b; break;             case '/': c=a/b; break;             }             gcvt(c, 16, szA);             i=strlen(szA)-1;             if (szA[i]=='。
  ') szA[i]='\0';             //把计算结果压入栈             i=0;             do NumPush(szA[i]);             while (szA[++i]!='\0');             NumPush(',');             break;          case '=':             s++;             break;          default:             error(order);             return false;          }       }    }while (p!=0);    result=atof(num);    return true; } void CalcInfixExp::error(char n) {    switch (n)    {    case '\1': printf("括号不匹配\n"); break;    case '\2': printf("右括号与左括号间没有运算符\n"); break;    case '\3': printf("低级括号内包含高级括号\n"); break;    case '\4': printf("运算符过多\n");    } } char CalcInfixExp::GetOrder(char a, char b) {    static char order[11][11]={       '>','>','<','<','<','>','<','>','<','>','>',       '>','>','<','<','<','>','<','>','<','>','>',       '>','>','>','>','<','>','<','>','<','>','>',       '>','>','>','>','<','>','<','>','<','>','>',       '<','<','<','<','<','=','\3','\1','\3','\1','\1',       '>','>','>','>','\2','>','>','>','>','>','>',       '<','<','<','<','<','\1','<','=','\3','\1','\1',       '>','>','>','>','\2','\3','=','>','>','>','>',       '<','<','<','<','<','\1','<','\1','<','=','\1',       '>','>','>','>','\2','\3','\2','\3','\2','>','>',       '<','<','<','<','<','\1','<','\1','<','\1','='    };    int i[2], j=0, TreatB=0;    do    {       switch (a)       {       case '+': i[j]=0; break;       case '-': i[j]=1; break;       case '*': i[j]=2; break;       case '/': i[j]=3; break;       case '(': i[j]=4; break;       case ')': i[j]=5; break;       case '[': i[j]=6; break;       case ']': i[j]=7; break;       case '{': i[j]=8; break;       case '}': i[j]=9; break;       case '\0': i[j]=10; break;       default: return '\0';       }       j++;       a=b;    }while (TreatB^=1);    return order[i[0]][i[1]]; } bool CalcInfixExp::NumPop(char &a) {    if (q==0) return false;    a=num[--q];    return true; } bool CalcInfixExp::OpePush(const char &a) {    if (p>=100) return false;    ope[p++]=a;    return true; } bool CalcInfixExp::OpePop(char &a) {    if (p==0) return false;    a=ope[--p];    return true; } int main() {    CalcInfixExp s;    double result;    char a[100];    while (gets(a))       if ( lc(result, a))          printf("%lg\n", result);    return 0; }。