为什么 x 是 5050？

Question

for(i = 1;i <= 100;i++)
    for(j = i; j <= 100; j++)
        x++;
System.out.println(x);

First I thought that the result would be 10.000, but it was 5050. Why? What does the i changes?

Answer 1

The answer 5050 is correct, given the assumption that x is 0 (as it appears based on your results). The reason it is not 10,000 is the line j = i instead of eg j = 1 , which makes it 100 + 99 + 98 + ... + 1 = 5050.

Answer 2

At first i is 1 , so j goes from 1 too 100 and the inner loop does 100 iterations, which means x is incremented 100 times.

The next time, i becomes 2 , so j goes from 2 to 100. That means 99 iterations and x is incremented 99 times and so on and so forth...

That's the sum of all numbers from 100 to 1, which is (100 * (100 + 1)) / 2 == 5050

Answer 3

The inner loop executes (100 - i) times on each iteration of the outer loop. ie when the value of i = 0 in the outer loop, the inner loop executes 100 times , when the value of i = 1 in the outer loop, the inner loop executes 99 times and so on and so forth. When adding all these values 100 + 99 + 98 + ... + 1 = 5050