定制四则运算

public class MathP {
    //想要出几道题目
    public static void main(String[] args) {

        Scanner input=new Scanner(System.in);
        int length = input.nextInt();
        for(int k=0;k<length;k++) {
    int i=(int)(1+Math.random()*(100-1+1));
    int j=(int)(1+Math.random()*(100-1+1));
    char[]ch ={'+','-','*','/'};
    Random r =new Random();
    int index = r.nextInt(ch.length);

        System.out.print(i);
        System.out.print(ch[index]);
        System.out.print(j);
        System.out.println('=');
    }