求助，为什么有一个scanf会卡住

#include<stdio.h>
int main()
{
int c,d;   
scanf("%d",&c);   
int a[20];
for(int i = 0 ; i < c ; i++){
        scanf("%d", &a[i]);   
}
scanf("%d",&d);//就是这个scanf卡住了，不读入数据，也不会继续执行
int b[20];   
for(int j = 0 ; j < d ; j++){
       scanf("%d", &b[j]);   
}
int flag;
int x = 0;
for(int m = 0 ; m < c ; m++){
        flag == 1;
        for(int n = 0 ; n < d ; n++){
            if(a[m] == b[n]){
                flag = 0;
                break;
            }
        }
        if(flag == 1){
            x++;   
    }
    }   
for(int n = 0 ; n < d ; n++){
        flag == 1;
        for(int m = 0 ; m < c ; m++){
            if(b[n] == a[m]){
                flag = 0;   
            break;
            }
        }
        if(flag == 1){
            x++;   
    }
    }
    int k[x];
    x = 0;   
for(int m = 0 ; m < c ; m++){
        flag == 1;   
    for(int n = 0 ; n < d ; n++){
            if(a[m] == b[n]){
                flag = 0;   
            break;
            }
        }
        if(flag == 1){
            k[x] = a[m];
            x++;   
    }
    }
for(int n = 0 ; n < d ; n++){
        flag == 1;
        for(int m = 0 ; m < c ; m++){
            if(b[n] == a[m]){
                flag = 0;   
            break;   
        }
        }
        if(flag == 1){
            k[x] = b[n];
            x++;   
    }
    }
    int i = 0;   
for(; i < x - 1 ; i++){
        flag = 1;        
for(int p = i + 1;p < x;p++){
            if(k[i] == k[p]){
                flag = 0;   
            break;   
        }
        }
        if(flag == 1){
            printf("%d ", k[i]);
        }
    }
    printf("%d", a[i]);
    return 0;
}