Java, for statement / while statement starting from beginner

Introduction

This article is a memorandum. Although it is a reference book level content, the code posted in this article is about ** Wrong ** are the main things. This is for the purpose of posting the part that was actually mistaken during coding and posting it for self-reflection. In addition, I will not touch on the deep part here because I will review it later while also studying the Java Silver exam questions.

environment

Language: Java11, JDK13.0.2 Operating environment: Windows 10

for statement

The ** for statement ** is one of the iterative processing statements for ** iterative processing ** until the loop is exited, based on the ** conditional statement **. It is suitable for repeating by specifying the number of times.

Basic form of for statement

for (Initialization statement; Conditional statement; Update statement){
　　　　　//Iterative processing;
}

Click here for each role.

• ** Initialization statement ** for statement A statement that declares a temporary variable used in internal iterative processing and initializes it. You can declare and initialize multiple variables ** by separating them with commas `,`, but all of them must be ** the same variable type ** (excluding variables declared outside the for statement). ).
• **Conditional statement**
**Boolean value**Using the formula that returns**Continue iterative processing (`true`）**Or**for文Orら抜ける(`false`)**Orを判定する文。Conditional statementを複数記述することはできないが、前回扱った**Logical AND`&&`・ Logical sum`||`**It is possible to set compound conditions using.
• ** Update statement ** A statement that describes the process for changing the value of a temporary variable after the iterative process is completed once. Like the initialization statement, it can ** handle multiple processes **. Particular attention should be paid to when and when the update will be applied.

amount10Years.java

double amount = 100000;

for (int year = 1; year < 10; year++){
  amount *= 1.02;
}
System.out.println("10 years later" + amount + "It becomes a circle.");

//Something is missing ...

In this case, the first year is the second year, and only nine compound interest calculations can be made. If you make a mistake in setting the initial value, it will affect the number of times.

while statement

Along with the for statement, it is a statement that repeats processing. It is suitable for repeating until the expected condition is reached, but be careful because it is easier to create ** infinite loop ** than for statement.

Basic form of while statement

while (Conditional statement){
　　　　　//Iterative processing;
}

For the conditional statement, see the one in the explanation of the for statement.

As another form, ** do ~ while statement ** also exists. Since the process is repeated at least once, it is recommended to use it when the essential process is included. Pay close attention to the position of the semicolon ;.

do~Basic form of while statement

do{
　//Iterative processing;
} while (Conditional statement);

while statement practice

whileAmount150k

double amount = 100000;
int year = 0;

//This time I properly set the first year to 0

while (amount <= 150000) {
    amount *= 1.02;
}
System.out.println(year + "It will exceed 150,000 yen over the years.");

//The target amount was reached in less than a year ...

This time, I didn't include year ++ in the processing of the while statement, so the final output became strange.

At the end

It's a very useful sentence, but it also carries the risk of ridiculous results if left misunderstood. I want to understand it well because it is used in areas such as interest rate calculation and algorithms that can never be mistaken. For this reference, I put a Java qualification test book, but it doesn't have {} (curly braces), the nesting structure is deep and it takes time to understand, increment ・ decrement Is spread in large quantities. There are good problems that require both comprehension and concentration.

reference

I write variables and expressions as much as possible and compile them, so if I want to quote them completely, I will describe that.

Easy Java 7th Edition

Java SE11 Silver Problem Collection (commonly known as Kuromoto)