我试着调试这个程序很久了。当我输入像a + b - c或a / b + c这样的表达式，其中第一个运算符的优先级大于或等于第二个运算符时，它可以正常工作。但是对于像a - b / c这样第一个运算符的优先级比第二个运算符的优先级低的表达式，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;
}
任何关于如何改进我的编码的建议都是有帮助的。
最佳答案
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;
}
`