c++算术表达式求值

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解决时间 2021-11-26 17:24

提问者网友：低吟詩仙的傷
2021-11-25 18:44

c++算术表达式求值

最佳答案

五星知识达人网友：污到你湿
2021-11-25 19:26

#include
#include
#include

#define MAXSIZE 100

//数字栈
typedef struct oprd{

    double data[MAXSIZE];
    int top;

}OPRD;

//运算符栈
typedef struct optr{

    char data[MAXSIZE];
    int top;

}OPTR;

//因为涉及到两个栈的操作,所以将栈相关的操作用宏定义写成函数,
//这样就具有了通用性
//初始化栈
#define InitStack(StackType, stack)
{
    *stack = (StackType *)malloc(sizeof(StackType));
    *stack->top = -1;
}

//判栈空
#define EmptyStack(stack)
(
    stack->top == -1
)

//判栈满
#define FullStack(stack)
(
    stack->top == MAXSIZE - 1
)

//入栈
#define PushStack(stack, value)
{
    if (!FullStack(stack)){
        stack->top++;
        stack->data[stack->top] = value;
    }
    else{
        printf("栈已满,无法入栈
");
        exit(-1);
    }
}

//出栈
#define PopStack(stack, value)
{
    if (!EmptyStack(stack)){
        *value = stack->data[stack->top];
        stack->top--;
    }
    else{
        printf("栈已空,无法出栈
");
        exit(-1);
    }
}

//取栈顶元素
#define GetStackTop(stack, value)
{
    if (!EmptyStack(stack)){
        *value = stack->data[stack->top];
    }
    else{
        printf("栈为空,无法取栈顶元素
");
    }
}

//优先级表
char compare(char ch, char top)
{
    switch(ch){
        case '+':
        case '-':
            if (top == '+' || top == '-' || top == '*' || top == '/')
                return '<'; //扫描的小于栈顶
            else
                return '>'; //扫描的大于栈顶
            break;
        case '*':
        case '/':
            if (top == '*' || top == '/')
                return '<';
            else
                return '>';
            break;
        case '(':
            if(top == ')'){
                printf("输入有误!
");  exit(-1);
            }
            return '>';
            break;
        case ')':
            if (top == '(')
                return '=';
            else if(top == '#'){
                printf("输入有误!
");
                exit(-1);
            }
            else{
                return '<';
            }
            break;
        case '#':
            return '<';
    }
}

//输入表达式并计算结果
double CalculateExp(void)
{
    double result, tempNum1, tempNum2;
    double data = 0, expn;
    char ch, topSign, point = 'n', num = 'n';
    OPTR *sign;
    OPRD *number;

    InitStack(OPTR, &sign);
    InitStack(OPRD, &number);
    PushStack(sign, '#');
    printf("请输入表达式：");
    ch = getchar();
    GetStackTop(sign, &topSign);

    while(ch != '#' || topSign != '#'){
        if ('0' <= ch && ch <= '9' || ch == '.'){
            if (ch == '.' && point == 'y'){
                printf("表达式输入有误!
");
                exit(-1);
            }
            else if (ch == '.' && point == 'n'){
                point = 'y';
                expn = 0.1;
            }
            else{
                if (point == 'y'){
                    data = data + expn * (ch - '0');
                    expn *= 0.1;
                }
                else{
                    data = data * 10 + (ch - '0');
                }
                num = 'y';
            }
            ch = getchar();
        }
        else if (ch == '+' || ch == '-' || ch == '*' || ch == '/' || ch == '(' || ch == ')' || ch == '#'){
            if (num == 'y'){
                PushStack(number, data);
                num = 'n';    point = 'n';
                data = 0;
            }
            GetStackTop(sign, &topSign);
            switch(compare(ch, topSign)){
                case '<':       //扫描运算符优先级小于栈顶元素
                    PopStack(sign, &topSign);
                    PopStack(number, &tempNum1);
                    PopStack(number, &tempNum2);
                    switch(topSign){
                        case '+':  result = tempNum1 + tempNum2;   break;
                        case '-':  result = tempNum1 - tempNum2;   break;
                        case '*':  result = tempNum1 * tempNum2;   break;
                        case '/':  result = tempNum2 / tempNum1;   break;
                    }
                    PushStack(number, result);
                    break;
                case '>':       //扫描运算符优先级大于栈顶元素
                    PushStack(sign, ch);
                    ch = getchar();
                    break;
                case '=':      //扫描运算符为右括号,匹配到了左括号
                    PopStack(sign, &topSign);
                    ch = getchar();
                    break;
            }
        }
        else if (ch == '
'){
            ch = '#';
        }
        else{
            printf("输入的表达式有误!
");
            exit(-1);
        }
        GetStackTop(sign, &topSign);
    }
    PopStack(number, &result); //将结果从栈中取出来
    if (!EmptyStack(number)){   //如果取出后栈不为空则表示输入的表达式不正确
        printf("表达式有误!
");
        exit(-1);
    }

    return result;
}

int main(void)
{
    printf("%lf
", CalculateExp());

    return 0;
}

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