数据结构课程设计 算术表达式求值

题目：编制一个用算符优先法对算术表达式求值的程序

//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][n])     {        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; }