Control flow statements: if and switch statements

Control flow statements: if and switch statements

In programming, control flow statements are a key concept, which are used to control the way and order of program execution. Control flow statements can change the execution order of the program based on conditions, allowing the program to perform different operations according to specific situations. Among them, if statement and switch statement are one of the most commonly used control flow statements.

if statement

The if statement is used to determine whether to execute some code based on a condition in the program. The syntax is as follows:

if (condition) {
  // 如果条件为真执行此处代码块
}

The condition represents an expression that can return a Boolean value (true or false). If the result of the expression is true, the code block after the if statement is executed. If the expression evaluates to false, this block of code is skipped.

The if statement can have an optional else clause that executes some code when the result of the expression is false. Its syntax is as follows:

if (condition) {
  // 如果条件为真执行此处代码块
} else {
  // 如果条件为假执行此处代码块
}

For example:

let x = 10;

if (x > 5) {
  console.log("x大于5");
} else {
  console.log("x小于或等于5");
}

switch statement

The switch statement is also a control flow statement that executes different codes based on conditional judgment, but it is different from if The difference is that the switch statement can judge multiple conditions and execute different code blocks. Its syntax is as follows:

switch (expression) {
  case value1:
    // 如果expression等于value1，执行此处代码块
    break;
  case value2:
    // 如果expression等于value2，执行此处代码块
    break;
  case value3:
    // 如果expression等于value3，执行此处代码块
    break;
  default:
    // 如果expression不等于任何一个value，执行这个默认代码块
}

where expression is the value to be tested, and the case statement is followed by possible values. When expression is equal to a certain value, the code block corresponding to the value will be executed, and Use the break statement to break out of the switch statement. default is used to execute this default code block when expression is not equal to any value.

For example:

let day = 3;

switch (day) {
  case 0:
    console.log("今天是星期日");
    break;
  case 1:
    console.log("今天是星期一");
    break;
  case 2:
    console.log("今天是星期二");
    break;
  case 3:
    console.log("今天是星期三");
    break;
  case 4:
    console.log("今天是星期四");
    break;
  case 5:
    console.log("今天是星期五");
    break;
  case 6:
    console.log("今天是星期六");
    break;
  default:
    console.log("请输入正确的星期数");
}

Summary

If and switch statements are ways to execute different code blocks based on conditions in control flow statements. The if statement is used to determine whether to execute a block of code based on a single condition, and optionally whether to execute an else clause. The switch statement can execute multiple different code blocks based on the expression value, and can have an optional default code block to handle situations where no case value can be matched. By using if and switch statements, the execution of the control program can be more flexible and rich.

The above is the detailed content of Control flow statements: if and switch statements. For more information, please follow other related articles on the PHP Chinese website!