express

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#include <stdio.h>#include <stdlib.h>#include <string.h>#include <ctype.h>const int Size = 50;char Stack[Size];char SuffixExpression[Size];    /*后缀表达式数组*/int top = -1;   /*始终指向栈顶*/int index = 0;  /*后缀表达式索引*//*----------------栈基本操作-------------*/void Push(char x)  /*压栈*/{if (top == Size-1){   printf("top=%d stack overflow\n", top);exit(1);}Stack[++top] = x;}char Pop()  /*出栈*/{if (top == -1){printf("top=%d stack overflow\n", top);exit(1);}return Stack[top--];}char GetTop() /*获取栈顶元素*/{if (-1 != top){return Stack[top];}return NULL;}bool Empty()  /*判断栈是否为空*/{return (top == -1 ?  1: 0);}/*------------计算结果-----------------*/int Calc(int num1, int num2, char op){switch(op){case '+':     return num1 + num2;    case '-':     return num1 - num2;    case '*':     return num1 * num2;    case '/':     if (0 == num2) { printf("The divisor is 0\n");    exit(1); }     return num1 / num2;        default:     return 0;}}/*-----------运算符优先级比较--------------*/int PriorityCompare(char op1, char op2){switch(op1){case '+':case '-':     return (op2 == '*' || op2 == '/' ? -1:0);case '*':case '/':     return (op2 == '+' || op2 == '-' ?  1:0);case '(': return 1;default: return 1;}return 1;}/*-----------判断字符是否是运算符---------*/int OperatorSymbol(char op){switch(op){    case '+':case '-':case '*':case '/':case '(':case ')':return 1;default :return 0;}return 0;}/*--------将中缀表达式转换成后缀表达式------------*/void ConvertSuffixExpression(const char* p){while(*p != '\0'){if(isdigit(*p))  /*处理数字*/{SuffixExpression[index++] = *p;p++;}else if(1 == OperatorSymbol(*p))  /*处理运算符*/{if (Empty())  /*栈为空，运算符直接入栈*/{Push(*p);p++;}else if ('(' == *p)   /*左括号直接压栈*/{Push(*p);p++;}else if(')' == *p)   /*右括号取出栈中()之间的运算符*/{while('(' != GetTop())   {SuffixExpression[index++] = GetTop();Pop();}Pop();   /* '(' 出栈*/p++;}else if(1==PriorityCompare(*p,GetTop()) || '('==GetTop())  /*当前运算符比栈顶运算符优先级高或栈顶为左括号则直接入栈*/{Push(*p);p++;}else{while (1!=PriorityCompare(*p,GetTop()) && !Empty())  /*栈顶运算符优先小于等于当前运算符优先级则出栈*/{if ('(' == GetTop())   /*栈顶为左括号*/{continue;}SuffixExpression[index++] = GetTop();Pop();}Push(*p);p++;}}else{printf("%c is invaild symbol\n", *p);exit(1);}}while(!Empty()){SuffixExpression[index++] = GetTop();Pop();}SuffixExpression[index++] = '\0';}/*------------根据后缀表达式计算结果----------*/int Calculate(){int i;char TempSum;int num1, num2;int len = strlen(SuffixExpression);for(i=0; i<len; i++){if (isdigit(SuffixExpression[i]))  /*数字直接压栈*/{Push(SuffixExpression[i]);}else if (OperatorSymbol(SuffixExpression[i])) /*当前符号是运算符则从栈中取出两个数运算，将结果继续压栈*/{num1 = GetTop()-'0';            Pop();num2 = GetTop()-'0';Pop();TempSum = Calc(num2, num1, SuffixExpression[i]) + '0';Push(TempSum);}}return GetTop()-'0'; /*栈顶值即为表达式值*/}int expr(const char* p){   if (NULL == p){printf("null pointer\n");exit(1);}memset(Stack, 0, Size);memset(SuffixExpression, 0, Size);ConvertSuffixExpression(p);return Calculate();}void main (){/*char *exp = "9+(3-1)*3+8/2";*//*char *exp = "1";*//*char *exp = "1+2";*//*char *exp = "3-2";*//*char *exp = "1+2+3";*//*char *exp = "3-2-1";*//*char *exp = "(1+2)-3";*/char *exp = "9*1+(2-1)+2*3";int sum = expr(exp);printf("%s\n", SuffixExpression); printf("%d\n", sum);}
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