c语言switchcasedefault(c语言switchcase怎么定范围)

1. Introduction

Switch case statements are powerful control structures in the C programming language. They provide a convenient way to execute different blocks of code based on the value of a variable or an expression. The 'switch' keyword is followed by the variable or expression being evaluated, and the 'case' keyword is used to define different possible values. The 'default' case is optional and is executed if none of the 'case' values match the evaluated expression. In this article, we will delve into the details of switch case statements and the usage of the 'default' case.

2. Working with Switch Case

The switch case statement is a more efficient and readable alternative to cascaded 'if-else' statements in situations where multiple conditions need to be tested against a single variable. The variable or expression following the 'switch' keyword is evaluated, and the control is transferred to the matching 'case' block. Each 'case' block contains a constant value or an expression that is compared to the evaluated variable or expression. If the comparison is true, the associated block of code is executed. The 'break' statement is used to terminate the execution of the 'case' block and to transfer the control to the next line of code after the entire switch case statement.

For example, let's consider a program that takes an integer representing the day of the week and prints out the corresponding name of the day:

#include <stdio.h>
int main() {
  int day = 2;
  switch(day) {
    case 1:
      printf("Monday");
      break;
    case 2:
      printf("Tuesday");
      break;
    case 3:
      printf("Wednesday");
      break;
    // more cases defined
    default:
      printf("Invalid day");
  }
  return 0;
}

In this example, the variable 'day' is evaluated, and the control is transferred to the matching 'case' block. The program will print "Tuesday" because the value of 'day' is 2. If the value of 'day' is not present in any of the 'case' blocks, the 'default' block will be executed, which prints "Invalid day". It is important to include a 'default' case to handle unexpected or invalid values.

3. The Default Case

The 'default' case is optional in a switch case statement. It is executed when none of the 'case' values match the evaluated expression. This is useful to handle unexpected or invalid values gracefully. The 'default' case acts as a catch-all case. Including a 'default' case is a best practice to ensure that the program does not terminate abruptly or provide unexpected results in such situations.

Let's modify the earlier example by assigning a value of 7 to the 'day' variable, which is not present in any of the 'case' blocks:

#include <stdio.h>
int main() {
  int day = 7;
  switch(day) {
    case 1:
      printf("Monday");
      break;
    case 2:
      printf("Tuesday");
      break;
    case 3:
      printf("Wednesday");
      break;
    default:
      printf("Invalid day");
  }
  return 0;
}

In this case, the program will print "Invalid day" since none of the 'case' blocks matches the value of 'day'. By providing a 'default' block, we ensure that the program does not terminate unexpectedly or provide incorrect output for invalid input values.

In conclusion, the switch case statement is a powerful control structure in the C programming language. It allows for concise and efficient handling of multiple conditions based on the value of a variable or an expression. The 'default' case is optional and provides a catch-all block of code to handle unexpected or invalid values. It is always recommended to include a 'default' case to ensure the program handles all possible scenarios gracefully.