for (i = 1; i < n; i++) {
num = a[i]; 
while(num < a[i - 1])
{
a[i] = a[i - 1];
break;
}
a[i] = num;
}

------解决方案--------------------
用一维数组来做直接插入排序，时间复杂度是O(n2),要用双层的循环，里面的循环是用来移动数组元素位置的。直接插入排序建议用链表实现。

------解决方案--------------------
public class method {
	public static void rank(int n) {
		int a[] = new int[n];
		Random rd = new Random();

		for (int i = 0; i < n; i++) {
			a[i] = rd.nextInt(1000);
		}

		int temp = 0;// 中间变量
		int min = 0;// 最小值
		int minIndex = 0;// 最小值下标
		for (int i = 0; i < a.length; i++) {
			min = a[i];
			minIndex = i;
			for (int j = i + 1; j < a.length; j++) {
				if (a[j] < min) {
					min = a[j];
					minIndex = j;
				}

			}
			temp = a[i];
			a[i] = a[minIndex];
			a[minIndex] = temp;
		}

		System.out.println("排序后数组为：");
		for (int i = 0; i < n; i++)
			System.out.print(a[i] + "\t");
	}

	public static void main(String args[]) {
		Scanner sc = new Scanner(System.in);
		System.out.println("输入随机数的个数");
		String str = sc.next();
		int n = Integer.parseInt(str);
		rank(n);
	}

}

------解决方案--------------------
Java code

//这里的循环有问题
for (i = 1; i < n; i++) {
num = a[i]; 
while(num < a[i - 1])
{
a[i] = a[i - 1];
break;
}
a[i] = num;
}