for迴圈

        int sum=0;
        for (int i = 100; i>=1; i--) {
            sum+=i;
        }
        System.out.println(sum);

while迴圈

        int sum=0;
        int i = 1;
        while(i<=100) {
            sum+=i;
            i++;
        }

do while迴圈

        int sum=0;
        int i=1;
        do {
            sum+=i;
            i++;
        }while(i<=100);