c语言scanf输入后直接退出

我设置了输入a和b，但输入a之后就直接退出了，为啥

#define _CRT_SECURE_NO_WARNINGS 1
#include <stdio.h>
#include<string.h>

int Max(int a, int b)
{
    if (a > b)
        return a;
    else(a > b);
        return b;
}
int main()
{

    int a = 0;
    int b = 0;
    printf("请输入a的值\n");
    scanf("%d", a);
    printf("请输入b的值\n");
    scanf("%d", b);
    int max = 0;
    max = Max(a, b);
    printf("%d\n", max);
    return 0;
}

这里有个之前做的，同样都是 打印→定义→输入，为啥我这个就不行

#define _CRT_SECURE_NO_WARNINGS 1
#include <stdio.h>
#include <Windows.h>

int main()
{
    printf("请输入轰炸的次数\n");
    int Message_Num;
    scanf("%d", &Message_Num);
    printf("请输入轰炸的对象\n");
    char num[10];
    scanf("%s", num);
    FindWindow(NULL, num);
    while (Message_Num>0)
   {
        SendMessage(FindWindow(NULL, num),WM_PASTE,NULL,0);
        SendMessage(FindWindow(NULL, num),WM_KEYDOWN,VK_RETURN,0);
        Message_Num--;
    }
    return 0;
}

输入里面少了&