[Error] ld returned 1 exit status 求问这个error怎么搞啊？？真的吐了。。

Question

链式堆栈完成中缀表达式到后缀表达式的转换
一直在gets函数报错，求问？？请问代码正确了吗。。

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

#define m 100
/* run this program using the console pauser or add your own getch, system("pause") or str loop */

typedef ElementType;
typedef struct SNode *PtrToSNode;
struct SNode {
    ElementType Data;
    PtrToSNode Next;
};
typedef PtrToSNode Stack;

Stack CreateStack( ) 
{ /* 构建一个堆栈的头结点，返回该结点指针 */
    Stack S;

    S = (Stack)malloc(sizeof(struct SNode));
    S->Next = NULL;
    return S;
}

int IsEmpty ( Stack S )
{ /* 判断堆栈S是否为空，若是返回true；否则返回false */
    return ( S->Next == NULL );
}

void Push( Stack S, ElementType X )
{ /* 将元素X压入堆栈S */
    PtrToSNode TmpCell;

    TmpCell = (PtrToSNode)malloc(sizeof(struct SNode));
    TmpCell->Data = X;
    TmpCell->Next = S->Next;
    S->Next = TmpCell;

}

ElementType Pop( Stack S )  
{ /* 删除并返回堆栈S的栈顶元素 */
    PtrToSNode FirstCell;
    ElementType TopElem;

    if( IsEmpty(S) ) {
        printf("堆栈空"); 
        return  0;
    }
    else {
        FirstCell = S->Next; 
        TopElem = FirstCell->Data;
        S->Next = FirstCell->Next;
        free(FirstCell);
        return TopElem;
    }
}

void change(Stack S, ElementType str[])
{
    int i =0;
    ElementType e;
    CreatStack();
    while(str[i]!='\0')
    {
        while(isdigit(str[i]))
        {
            printf("%c",str[i++]);
            if(!isdigit(str[i]))
            {
                printf(" ");
            }
        }
        if(str[i]=='+'||str[i]=='-')
        {   
            if(S->Next=NULL)
            {
            Push(S,str[i]); 
            }   
        else
        {
            do
            {
                Pop(S);
                if(e=='(')
                {
                    Push(S, e);
                }
                else
                {
                    printf("%c",e);
                }
            }
            while(e!='(');
            {
                Push(S,str[i]);
            }
        }
    }
        else if(str[i]==')')
        {
            Pop( S);
            while(e!='(')
            {
                printf("%c",e);
                Pop(S);
            }
        }
        else if(str[i]=='*'||str[i]=='/'||str[i]=='(')
        {
            Push(S,str[i]);
        }
        else if(str[i]=='\0')
        {
            break;
        }
        else
        {
            printf("\n输入格式有误\n");
            return;
        }
        i++;
    }
    while (str[i]='\0')
    {
        Pop(S);
        printf("%c",e);
    }
}

int main(int argc, char *argv[]) {
    ElementType str[m];
    gets(str);
    Stack S;
    change(S,str);
    return 0;
}

Answer 1

加上
#include <ctype.h>

typedef ElementType;
->
typedef char ElementType;

CreatStack();
->
CreateStack();