这个为什么我想输入‘+’然后输出一个‘+’却不行

#include <stdio.h>
#include <stdlib.h>
#include
using namespace std;

typedef char DataType;

typedef struct Stack {
DataType* a;
int top;
}Stack;

void StackInit (Stack* S)
{
S->a = NULL;
S->top = 0;
}

void StackPush (Stack* S, DataType x)
{
if (S->a == NULL)
S->a = (DataType*)malloc(10000*sizeof(DataType));

S->a[S->top] = x;
S->top ++;
}

DataType StackTop (Stack* S)
{
if (S->top != 0)
return S->a[S->top - 1];
}

int main ()
{
Stack st;
DataType c;
StackInit (&st);
cin >> c;
StackPush (&st, c);
cout << StackTop (&st));
return 0;
}

cout << StackTop (&st)); 这里多了个括号，应该编译不过啊
还有一般这里最好 S->a = (DataType*)malloc(10000*sizeof(DataType)); 判断一下是否成功了