这是我第一次学习编程。我是大学一年级学生。我的专业是软件工程。这是我的第三个软件类任务。 老师希望该程序从命令行读入中缀表达式并输出后缀表达式。我们应该使用“Shunting Yard算法”。我们应该有2个链表队列和1个链表栈。用于保持输入和输出的2个队列和用于保持操作员的堆栈。我们也应该编写我已经做过的一般入队，出队，弹出，推送功能。
Shunting Yard算法：
该计划应如下运作： programename 34/5 + 16 * 2 后缀：34 5/16 2 * + 我们还应该在每个输出之间留出空间
对于初学者来说，这对我来说太难了。我已经在这个计划上花了超过30个小时。但该计划不起作用。程序继续在main函数的“while”循环中运行，永不停止。如果有人可以帮助我，我会非常感激。
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
struct listnode {
//Define structure of the node
char *element;
struct listnode* pnext;
};
struct Stack {
//Define structure of the stack
struct listnode* ptop;
};
struct Queue {
//Define structure of the queue
struct listnode* pfront;
struct listnode* prear;
};
void push (struct Stack* stack,char* element);
char* pop (struct Stack* stack);
void enqueue(struct Queue* queue,char* element);
char* dequeue(struct Queue* queue);
void s_travel(struct Stack* stack);
void q_travel(struct Queue* stack);
int precedence(char* x);
int empty(struct Stack* stack);
char* peek(struct Stack* stack);
int main (int argc,char *argv[]) {
struct Stack stack;
struct Queue input_queue;
struct Queue output_queue;
stack.ptop = NULL;
input_queue.pfront = NULL;
input_queue.prear = NULL;
output_queue.pfront = NULL;
output_queue.prear = NULL;
if (argc<3) {
//If the arguments is less then 3, unavailable input
printf("Input error");
return -1;
}
int i=0;
//Put all the arguments into the input_queue
for (i=1;i<argc;i++) {
enqueue(&input_queue,argv[i]);
}
printf("infix expression is : ");
q_travel(&input_queue);
printf("at the beginning, the peek of the stack is %s \n",peek(&stack));
for (i=1;i<argc;i++) {
//Token from input_queue
char *token;
char *x;
token = dequeue(&input_queue);
if(atof(token)) {
//If the element is a number,put it into output_queue
enqueue(&output_queue,token);
}
else {
/*If the element is a operator, c
* ompare the precedence of the top element of the stack and the precedence of token element
*/
char *peek1;
peek1=peek(&stack);
while ((precedence(peek1) >= precedence(token)) && (peek1 != NULL)){
/*while the precedence of the top element of the stack is greater
and equal to the precedence of token element*/
printf("inside,the top of the stack is %s \n",peek1);
//Pop element out of the stack and put it into output_queue
x = pop(&stack);
printf("after pop,x is %s,the top of the stack is %s \n",x,peek1);
enqueue(&output_queue,x);
}
//Then, push the new operator(token) into the stack
push(&stack,token);
}
}
while(peek(&stack)!=NULL) {
//Enqueue remaining operator from stack into output_queue
char *elem = pop(&stack);
enqueue(&output_queue,elem);
}
printf("Postifx expression is :\n");
q_travel(&output_queue);
return 0;
}
void push (struct Stack* stack,char* element) {
//Allocate a new node
struct listnode* new_node = (struct listnode *)malloc(sizeof(struct listnode));
new_node->element = element;
//Add new node at the top of the stack
new_node->pnext = stack->ptop;
stack->ptop = new_node;
}
char* pop (struct Stack* stack_buffer) {
//If the stack is not empty
if (stack_buffer->ptop) {
//Create a temporary node to replace top(removed) node
struct listnode *pelem = stack_buffer->ptop;
//The top pointer points to the next node
stack_buffer->ptop = pelem->pnext;
//Store the element of the removed node
char *elem = pelem->element;
//Remove node from memory
free(pelem);
//Return the element of the node that we removed
return elem;
}
//If the stack is empty, removing element fails,return -1
else {
return NULL;
}
}
void enqueue(struct Queue* queue,char *element) {
//Allocate a new node
struct listnode *new_node = (struct listnode *)malloc(sizeof(struct listnode));
new_node->element = element;
new_node->pnext = NULL;
//If the queue is not empty,add new node at the end of the queue
if (queue->prear) {
queue->prear->pnext = new_node;
}
//If the queue is empty,add new node at front of the queue
else {
queue->pfront = new_node;
}
//Added node becomes new rear node
queue->prear = new_node;
}
char* dequeue(struct Queue* queue) {
/*Create a temporary node to replace the front node of the queue
struct listnode *pelem = queue->pfront;*/
//If the queue is not empty
if (queue->pfront) {
//Store the element of the front node
char *elem = queue->pfront->element;
//The front pointer points to the next node
queue->pfront = queue->pfront->pnext;
//If the queue only has one node
if(pelem == queue->prear) {
//After removing the only node, the queue becomes empty
queue->prear = NULL;
}
//Remove node from memory
free(pelem);
//Return the element of the node that we removed
return elem;
}
//If the queue is empty, removing node fails,return NULL
else {
return NULL;
}
}
void s_travel(struct Stack* buffer) {
//Function to print out the element in the stack
//Create a temporary node to replace the top node of the stack
struct listnode* elem = buffer->ptop;
while(elem != NULL) {
printf("%s ", elem->element);
elem = elem->pnext;
}
printf("\n");
}
void q_travel(struct Queue* buffer) {
//Function to print out the element in the queue
//Create a temporary node to replace the front node of the stack
struct listnode* elem = buffer->pfront;
while(elem != NULL) {
printf("%s ", elem->element);
elem = elem->pnext;
}
printf("\n");
}
int precedence(char* operator) {
/*Function to determine the precedence of the operator,prior operator has greater return value*/
printf("entering precedence with %s \n",operator);
if (operator == NULL) {
return -1;
}
else if (strcmp(operator,"(")==0){
printf("Pr: %s 0\n",operator);
return 0;
}
else if (strcmp(operator,"+")==0||strcmp(operator,"-")==0) {
printf("Pr: %s 1\n",operator);
return 1;
}
else if ( (strcmp(operator,"*")==0) || (strcmp(operator,"/")==0) || (strcmp(operator,"%")==0) || (strcmp(operator,"x")==0) ) {
printf("Pr: %s 2\n",operator);
return 2;
}
else {
return -2;
}
return -3;
}
int empty(struct Stack* stack) {
//Function to check if the stack is empty
//If the stack is empty, the return value would be 1;otherwise, it would be 0
return NULL == stack->ptop;
}
char* peek(struct Stack* stack) {
//Function to find out the top element of the stack
//If the stack is empty, return NULL
if (empty(stack)) {
return NULL;
}
//If the stack is not empty, return the top element of the stack
char* elem = stack->ptop->element;
return elem;
}