c-试图实现一个结构堆栈

我的任务是：

编写一个程序来执行以下堆栈操作：创建一个带有项目代码和数量的堆栈

Itemcode    Quantity
    111     450
    112     0
    113     487
    114     101
    115     500
    116     0
    117     359

然后删除数量为零的项目并更新堆栈。

我的代码是：

#include<stdio.h>
#define LEN 7
struct item { int* num ; int* q; }
int main(void){
    int length = LEN,i,j;
    struct item data[LEN];
    // read input data into struct
    for(i=0 ; i < LEN ; i++){
        printf(" %d . enter item-code : ",i);
        scanf("%d",data[i].num);
        printf(" %d . enter quantity : ",i);
        scanf("%d",data[i].num);
    }
    // Delete the items having quantity zero and update the stack
    for(i=0 ; i < length ; i++) if(*data[i].q == 0){
        for(j=i+1;j<length;j++) 
            data[j-1] = data[j]; // update by overwriting
        data[j] = NULL;
        length--;
    }
    // display stack
    for(i=0 ; i < length && data[i]!= NULL; i++){
        printf(" %d > item : %d , quantity : %dn",i,*data[i].num,*data[i].q);
    }
    return 0;
}

这是我第一次用C语言处理structs。我得到的错误是：

StructStack.c:5: error: two or more data types in declaration specifiers
StructStack.c: In function 'main':                                                                   
StructStack.c:21: error: incompatible types when assigning to type 'struct item' from type 'void *'  
StructStack.c:26: error: invalid operands to binary != (have 'struct item' and 'void *')             
StructStack.c:30: error: incompatible types when returning type 'int' but 'struct item' was expected

任何帮助都会很棒。

问候Somjit。