Question

我一直在尝试调试这个程序很长一段时间。当我输入像a + b - c或a / b + c这样的表达式时，它工作正常，其中第一个运算符的优先级大于或等于第二个运算符。但是对于像a - b / c这样的表达式，其中第一个运算符的优先级低于第二个运算符，编译器会抛出一个断点。

struct stack
{
    char ele;
    struct stack *next;
};

void push(int);
int pop();
int precedence(char);

struct stack *top = NULL;

int main()
{
    char infix[20], postfix[20];
    int i = 0, j = 0;

    printf("ENTER INFIX EXPRESSION: ");
    gets(infix);

    while(infix[i] != '\0')
    {
        if(isalnum(infix[i]))
            postfix[j++] = infix[i];
        else
        {
            if(top == NULL)
                push(infix[i]);

            else
            {
                while( top != NULL && 
                      (precedence(top->ele) >= precedence(infix[i])) ) 
                    postfix[j++]=pop();
                push(infix[i]);
            }
        }

        ++i;
    }

    while(top != NULL)
        postfix[j++] = pop();

    postfix[j] = '\0';
    puts(postfix);
    getchar();
    return 0;
}

int precedence(char x)
{
    switch(x)
    {
    case '^': return 4;
    case '*':
    case '/': return 3;
    case '+':
    case '-': return 2;

    default: return 0;
    }
}

void push(int x)
{
    int item;
    struct stack *tmp;

    if(top == NULL)
    {
        top = (struct stack *)malloc(sizeof(struct stack));
        top->ele = x;
        top->next = NULL;
    }

    else
    {
        tmp = top;
        top->ele = x;
        top->next = tmp;
    }
}

int pop()
{
    struct stack *tmp;
    int item;

    if(top == NULL)
        puts("EMPTY STACK");

    else if(top->next == NULL)
    {
        tmp = top;
        item = top->ele;
        top = NULL;
        free(tmp);
    }

    else
    {
        tmp = top;
        item = top->ele;
        top = top->next;
        free(tmp);
    }

    return item;
}

有关如何改进编码的任何建议都会有所帮助。

Answer 1

it works fine for me.


#include<stdio.h>
#include<stdlib.h>
#include<string.h>

struct node
{

char data;
struct node *next;


}*top=NULL,*pstart=NULL;
/*-------------------- insertion in postfix expression linked list -------*/


void insert(char ch)
{
struct node *t,*baby;
    baby=(struct node *)malloc(sizeof(struct node));
    baby->next=NULL;
    baby->data=ch;
    t=pstart;

    if(pstart==NULL)
    {
    pstart=baby;
    }
    else
    {
    while(t->next!=NULL)
    t=t->next;
    t->next=baby;

    }
    //printf(" inserted in list- %c",baby->data);

}

/* --------- push operation ------- */



void push (char symbol)
{

    struct node *p;
    p=(struct node *)malloc(sizeof(struct node));
    p->data=symbol;
    if(top==NULL)
    {
     top=p;
     p->next=NULL;

    }
    else
    {

    p->next=top;
    top=p;

    }
}

char  pop()
{
struct node *x,*y;
char k;
if(top==NULL)
{
    printf("stack underflow\n");
    return 0;

}
else
{
x=top;
top=top->next;
k=x->data;
//printf("node %d is deleted\n",top->data);
free(x);
x=NULL;
return k;


}



}


void displaypost()
{
    struct node *to;
    if(pstart==NULL)
    printf("");
    else`enter code here`
    {
    to=pstart;
    while(to!=NULL)
    {
        printf("%c",to->data);
        to=to->next;

    }

    }


}


/*============== precedence selector ================= */

int precedence(char ch)
{

if(ch=='^')
return (5);
else if(ch=='*' || ch== '/')
return (4);
else if (ch== '+' || ch== '-')
return (3);
else
return (2);
}


/*=================== infix to postfix conversion ================ */

void intopost(char infix[])
{

    int len;
    int index=0;
    char symbol,temp;
    len= strlen(infix);
    //printf("%d",len);
    while(len>index)
    {
        symbol=infix[index];

        switch(symbol)
        {

        case '(':
        push(symbol);
        break;

        case ')':
        temp=pop();
        while(temp!='(')
        {
        insert(temp);
        temp=pop();
        }
        break;

        case '^':
        case '+':
        case '-':
        case '*':
        case '/':
        if(top==NULL)
        {
            push(symbol);
    //      break;

        }
        else
        {
        while(top!=NULL && (precedence(top->data)>=precedence(symbol)))
        {
            temp=pop();
            insert(temp);

        }
        push(symbol);

        }   
        break;
        default:
        insert(symbol);

         }
         index=index+1;


    }
    while(top!=NULL)
    {
    temp=pop();
    insert(temp);

    }
    displaypost();
    return;




}


int main()
{
char infix[50];
system("clear");
printf("enter infix expression: ");
gets(infix);

printf("\n\n equivalent postfix expression is---> ");
intopost(infix);
getchar();
return 0;
}
`

使用链表进行后缀实现的中缀

1 个答案: