A brief introduction to Java loop structures: while loop and do while loop

java loop structure

There are not many loop structures used in java. With the deepening of learning, you are more inclined to use loop thinking, as long as you master this kind of thinking , the loop can be used very flexibly

1. while loop: a straightforward operation that is repeatedly performed under a certain condition

2. do while loop: Compared with the while loop, the do while loop is executed first, and then judged

3. for loop: Under certain conditions, an operation is performed with a certain regularity

1. while loop

• while(Boolean expression){

• Loop body; // As long as the expression result is true, the loop content is executed

• }

2. do while loop

• do{

• Loop body; //Execute the loop once, and then determine the expression result

• }while(Boolean expression) ;

3. for loop

• for (initialization①; Boolean expression②; loop condition update④){

• Loop body ③; //The execution sequence is as marked above. As long as the Boolean expression is still satisfied after the loop condition is updated, the loop body will continue to be executed.

• }

4. Special: Enhanced for loop // Mainly used for array traversal, that is, starting from the subscript 0 to the last data

• for (declaration variable: array name) {

• System.out.println(variable name); //The size of the variable name does not need to be defined. In this loop, it will be customized as The length of the array -1

• }

The basic structural pattern is very simple. If you want to use the loop body flexibly, you need to pass A large number of questions are provided for training and this kind of thinking; here are some questions for everyone to experience for themselves, and I will publish the answers in the future.

1. Find the cumulative value of the integers 1 to 100, but it is required to skip all numbers with a single digit of 3.

2. Input a positive integer N, determine whether the number is a prime number, if it is a prime number, output "N is a prime number", otherwise output "N is not a prime number". Tip: The meaning of a prime number: it is not divisible by any number except 1 and itself.

3. Print out a pyramid pattern of n lines on the screen, for example, if n=5,The pattern is as follows:
   

# ***** *******
*********


## 5.Lucky guess: The game randomly gives a number from 0 to 99 (including 0 and 99), and then asks you to guess what number it is. You can guess a number at random, and the game will tell you whether it's too big or too small, narrowing down the results. After several guesses and hints, the answer was finally revealed. During the game, record the number of times you finally guessed correctly, and announce the result after the game is over.

Tips: Generate random numbers between 0 and 99: int number = (int)(Math.random()*100) 6. Enter two positive integers m and n, Find their greatest common divisor and least common multiple. 7. Find the value of s=a aa aaa aaaa aa...a, where a is a number. For example, 2 22 222 2222 22222 (a total of 5 numbers are added at this time), and the addition of several numbers is controlled by the keyboard.

8. A ball falls freely from a height of 100 meters. Each time it hits the ground, it bounces back to half of its original height. When it falls again, how many meters does it pass in total when it hits the ground for the 10th time? How high is the 10th rally?

9. There are four numbers 1, 2, 3, and 4. How many different three-digit numbers can be formed without repeated numbers? How many are they?

10. Request the output sequence 1 2 3 5 8 13 21 .......

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