1. for loop statement
The characteristics of circular structure: do something repeatedly and have the signs of start and end
//Format:
for(Initialization statement;Environment judgment statement;Conditional control statement){
Loop body statement;
}
/*Execution process
①: Execute initialization statement
②: Execute the conditional judgment statement to see whether the result is true or false
If false, the loop ends;
If true, continue to execute;
③: Execute loop body statement
④: Execute conditional control statements
⑤: Go back to ② and continue
*/
//example
public class hello{
public static void main(String[] args){
//Requirements: output hello world five times on the console
for(int i=0;i<5;i++) {
System.out.println("hello world");
}
}
}
/*Dead loop format
foe(::){
Loop body statement;
}
ctrl+c End dead cycle
*/
1. Case: summation
Requirements: sum the data between 1-5, and output the sum result on the console
public class hello{
public static void main(String[] args){
//Requirements: sum the data between 1-5, and output the sum result on the console
int sum = 0;//Define and initialize sum
for(int i=1;i<=5;i++) {
sum+=i;
}
System.out.println("sum:"+sum);
}
}
2. Case: even sum
Requirements: find the even sum between 1-100, and output the sum result on the console
public class hello{
public static void main(String[] args){
//Requirements: find the even sum between 1-100, and output the sum result on the console
int sum = 0;//Define and initialize sum
for(int i=1;i<=100;i++) {
if((i%2)==0) {
sum+=i;
}
}
System.out.println("sum:"+sum);
}
}
3. Case: daffodils
Requirement: output all "daffodils" on the console
Number of daffodils: ①: the number of daffodils is a three digit number
②: the cube sum of the number of daffodils, ten digits and hundred digits is equal to the original number.
Tip: how to calculate the value in the specified bit of any number:
First use the division operation to move the required number to one bit, and then use the remainder operation to get the value on the last bit;
For example, take 2 on the tenth bit of 123, divide 10 first, and get 12; Then take the remainder of 12 to get 2
public class hello{
public static void main(String[] args){
//Requirement: output all "daffodils" on the console
for(int i=100;i<1000;i++) {
int a = i%10;//Bit
int b = (i/10)%10;//Ten
int c = i/100;//Hundredth
if((a*a*a+b*b*b+c*c*c)==i) {
System.out.println(i+":It's daffodils");
}
}
}
}
2. while loop statement
//Basic format
while(Conditional judgment statement){
Loop body statement;
Conditional control statement;
}
/*Execution process:
①: Execute initialization statement
②: Execute the conditional judgment statement to see whether the result is true or false
If false, the loop ends
If true, continue
③: Execute loop body statement
④: Execute conditional control statements
⑤: Go back to 2 and continue
*/
public class hello{
public static void main(String[] args){
//Requirements: output hello world five times in a row on the console
int i = 0;
while(i<5) {
System.out.println("hello world");
i++;
}
}
}
/*Dead loop format:
while(true){
Loop body statement;
}
ctrl+c End dead cycle
*/
1. Case: Mount Everest
Demand: the highest peak in the world is Mount Everest (8844.43 M = 8844431 mm). I have a piece of paper large enough, and its thickness is 0.1 mm. How many times can I fold it to the height of Mount Everest?
public class hello{
public static void main(String[] args){
//Demand: the highest peak in the world is Mount Everest (8844.43 M = 8844431 mm). I have a piece of paper large enough, and its thickness is 0.1 mm. How many times can I fold it to the height of Mount Everest?
double paperh = 0.1;//Record the height of the paper
int zm = 8844431;//The height of Mount Everest
int n = 0;//Record the number of folds
while(paperh<=zm) {
paperh *= 2;
n++;
}
System.out.println("Folding required:"+n+"second");
}
}
3. do... while loop statement
//Format:
do{
Loop body statement;
Conditional control statement;
}while(Conditional judgment statement);
/*Execution process:
①: Execute initialization statement
②: Execute loop body statement
③: Execute conditional control statements
④: Execute the conditional judgment statement to see whether the result is true or false
If true, continue to execute;
If false, end the loop;
⑤: Go back to ② continue
*/
//example
public class hello{
public static void main(String[] args){
//Requirement: output hello world five times
int i = 0;
do {
System.out.println("hello world");
i++;
}while(i<5);
}
}
/*be careful:
do......while The difference between loop and for, while loop: whether the conditional judgment statement is true or not, the do... While loop body statement must be executed at least once.
*/
/*Dead loop format
do{
Loop body statement;
}while(true);
ctrl+c End dead cycle
*/
4. Jump control statement
//Continue is used in a loop. Based on condition control, skip the execution of the contents of a loop body and continue to execute the next loop //break is used in a loop. Based on conditional control, it ends the current whole loop and executes the statements behind the loop body
5. Loop nesting
Requirements: output the hours and minutes of the day on the console
Range of hours and minutes: 0 < = hours < 24;
0 < = min < 60;
public class hello{
public static void main(String[] args){
//Requirements: output the hours and minutes of the day on the console
for(int i=0;i<24;i++) { //Outer circulation control hour
for(int j=0;j<60;j++) { //Inner circulation control minutes
System.out.println("Hours and minutes of the day:"+i+"Time"+j+"branch");
}
}
}
}
6. Random
Random function: used to generate a random number
//Use steps //① Guide Package import java.util.Random(); //② Create object: r is the variable name, which can be changed, and the rest cannot be changed Random r = new Random; //③ Get random number: number is the variable name, which can be changed, the number 10 can be changed, and the rest cannot be changed int number = r.nextInt(10);//10 indicates the range of data obtained: [0,10)
//example
//① Guide Package
import java.util.Random;
public class hello{
public static void main(String[] args){
//② Create object: r is the variable name, which can be changed, and the rest cannot be changed
Random r = new Random();
//③ Get random number: number is the variable name, which can be changed, the number 10 can be changed, and the rest cannot be changed
int number = r.nextInt(10);//10 indicates the range of data obtained: [0,10)
//Output random number
System.out.println(number);
//Requirement: randomly generate a random number from 1 to 100
int a = r.nextInt(100)+1;
System.out.println(a);
}
}
1. Case: guess the number
Requirements: the program automatically generates a number between 1-100, and uses the program to guess the number.
When you guess wrong, give corresponding tips according to different situations
①: if the guessed number is larger than the real number, it indicates that the guessed number is larger.
②: if the guessed number is smaller than the real number, it indicates that the guessed number is smaller.
③: if the number you guessed is equal to the real number, you will be prompted to congratulate you on your correct guess
import java.util.Scanner;
import java.util.Random;
public class hello{
public static void main(String[] args){
//Requirements: the program automatically generates a number between 1-100, and uses the program to guess the number.
Random r = new Random(100)+1;
Scanner sc = new Scanner(System.in);
int number = r.nextInt(10);//Randomly generated number
int i = 0;//Record the number of guesses
while(true) {
i = sc.nextInt();//Enter the number of guesses
//Judge the guess and prompt according to the situation
if(number==i) {
System.out.println("Congratulations, you guessed right");
break;//Jump out of the loop
}else if(number>i) {
System.out.println("Your guess is too small");
}else if(number<i) {
System.out.println("Your guess is too big");
}
}
}
}