(Huawei trial) Evaluate the string conditional expression using a two-way linked list

Description: calculates the value of an arithmetic expression in string format.
Expressions support the following operations: "+,-, *,/". The priority of "*" and "/" is higher than that of "+" and "-".
Parentheses are not required and there is no space between expressions;
For example, for the expression "3-2 + 15*2", the expression value is 31.
Run Time Limit: 60 sec
Memory limit: 256 Mbyte
Input: subtraction, multiplication, division, and four arithmetic expressions. The length cannot exceed 1024 bytes. The formula does not contain parentheses or spaces.
Output: Operation Result of the expression.
Example input: 3-2 + 15*2

Sample output: 31

#include <stdio.h>#include <string.h>#include <stdlib.h>struct ListNode{int m_nValue;char m_nChar;ListNode* m_pNext;ListNode* m_pPrev;};ListNode* CreatNode(int m_nValue,int m_nChar,ListNode* m_pPrev,ListNode* m_pNext){ListNode* m_pNode=new ListNode();m_pNode->m_nChar=m_nChar;m_pNode->m_nValue=m_nValue;m_pNode->m_pNext=m_pNext;m_pNode->m_pPrev=m_pPrev;return m_pNode;}void DestroyList(ListNode* pHead){ListNode* pNode=pHead;while(pNode!=0){pHead=pNode->m_pNext;free(pNode);pNode=pHead;}}int StrCalculate(char* str){if(str==NULL)return -1;int tmp=0;int len;int i,k=0;ListNode* head=NULL;ListNode* p=NULL;ListNode* q=NULL;p=q=head=(ListNode*)malloc(sizeof(ListNode));len=strlen(str);for(i=0;i<len;i++){tmp=0;while(str[i]>='0'&&str[i]<='9'){tmp=tmp*10+str[i]-'0';++i;}if(k==0){head=CreatNode(tmp,'0',NULL,NULL);p=head;}else{q=CreatNode(tmp,'0',p,NULL);p->m_pNext=q;p=q;k++;}if(i<len){q=CreatNode(0,str[i],p,NULL);p->m_pNext=q;p=q;k++;}elsebreak;}p=head;while(p->m_pNext!=NULL){if(p->m_nChar=='*'){tmp=p->m_pPrev->m_nValue * p->m_pNext->m_nValue;p->m_pPrev->m_nValue=tmp;if(p->m_pNext->m_pNext!=NULL){p->m_pPrev->m_pNext=p->m_pNext->m_pNext;p->m_pNext->m_pNext->m_pPrev=p->m_pPrev;}else{ p=p->m_pPrev;p->m_pNext=NULL;break;}}else if(p->m_nChar=='/'){tmp=p->m_pPrev->m_nValue/p->m_pNext->m_nValue;p->m_pPrev->m_nValue=tmp;if(p->m_pNext->m_pNext!=NULL){p->m_pPrev->m_pNext=p->m_pNext->m_pNext;p->m_pNext->m_pNext->m_pPrev=p->m_pPrev;}else{p=p->m_pPrev;p->m_pNext=NULL;break;}}p=p->m_pNext;}p=head;while(p->m_pNext!=NULL){if(p->m_nChar=='+'){tmp=p->m_pPrev->m_nValue+p->m_pNext->m_nValue;p->m_pNext->m_nValue=tmp;}else if(p->m_nChar=='-'){tmp=p->m_pPrev->m_nValue-p->m_pNext->m_nValue;p->m_pNext->m_nValue=tmp;}p=p->m_pNext;}tmp=p->m_nValue;printf("the result is : %d\n",tmp);DestroyList(head);return tmp;}int main(){char* m_str="2-3-12/2*4";StrCalculate(m_str);return 0;}