C++| Ingenious work from 0 to 1 introductory programming [video + courseware + notes + source code]
table of Contents
1. Switch statement [C language]
1.2, the syntax of the switch statement in C language
1.3, switch statements follow the rules
1. Switch statement [C language]
Novice tutorial C language switch statement: https://www.runoob.com/cprogramming/c-switch.html
A switch statement allows testing when a variable is equal to multiple values. Each value is called a case, and the variable being tested will be checked for each switch case .
1.2, the syntax of the switch statement in C language
switch (expression) {
case constant-expression :
statement(s);
break; /* 可选的 */
case constant-expression :
statement(s);
break; /* 可选的 */
/* 您可以有任意数量的 case 语句 */
default : /* 可选的 */
statement(s);
}1.3, switch statements follow the rules
The switch statement must follow the following rules:
- The expression in the switch statement is a constant expression and must be an integer or enumerated type .
- There can be any number of case statements in a switch. Each case is followed by a value to be compared and a colon.
- The constant-expression of the case must have the same data type as the variable in the switch, and it must be a constant or a literal.
- When the tested variable is equal to the constant in the case, the statement following the case will be executed until the break statement is encountered .
- When a break statement is encountered , the switch is terminated and the control flow will jump to the next line after the switch statement.
- Not every case needs to include break . If the case statement does not contain break , the control flow will continue with subsequent cases until break is encountered.
- A switch statement can have an optional default case, which appears at the end of the switch. The default case can be used to perform a task when none of the above cases are true. The break statement in the default case is not necessary.
1.3, switch flow chart
1.4, switch instance
#include <stdio.h>
int main()
{
char grade = 'B'; /* 局部变量定义 */
switch (grade)
{
case 'A':
printf("很棒！\n");
break;
case 'B':
case 'C':
printf("做得好！\n");
break;
case 'D':
printf("您通过了！\n");
break;
case 'F':
printf("最好再试一下！\n");
break;
default:
printf("无效的成绩！\n");
}
printf("您的成绩是 %c！\n", grade);
return 0;
}2. Switch statement [C++]
2.1, role
Execute multiple conditional branch statements.
2.2, grammar
switch (表达式) //【switch语句中表达式类型只能是整型或者字符型】
{
case 结果1: 执行语句;break;
case 结果2: 执行语句;break;
...
default: 执行语句;break;
}2.3. Example
#include <iostream>
using namespace std;
int main() //switch语句
{
//请给电影进行评分
// 10 ~ 9 经典
// 8 ~ 7 非常好
// 6 ~ 5 一般
// 5分以下 烂片
//1、提示用户给电影评分
cout << "请给电影打分：" << endl;
//2、用户开始进行打分
int score = 0;
cin >> score;
cout << "您打的分数为：" << score << endl;
//3、根据用户输入的分数来提示用户最后的结果
switch (score)
{
case 10:
// cout << "您认为是经典电影！" << endl;
// break; //退出当前分支
case 9:
cout << "您认为是经典电影！" << endl;
break; //退出当前分支
case 8:
// cout << "您认为电影非常好！" << endl;
// break;
case 7:
cout << "您认为电影非常好！" << endl;
break;
case 6:
case 5:
cout << "您认为电影一般！" << endl;
break;
default:
cout << "您认为是烂片！" << endl;
break;
}
//if和switch区别?
//switch缺点：判断时候只能是整型或者字符型，不可以是一个区间！
//switch优点：结构清晰，执行效率高！
system("pause");
return 0;
}2.4. Precautions and summary
- Note 1: The expression type in the switch statement can only be integer or character type .
- Note 2: If there is no break in the case, the program will be executed all the way down.
- Summary: Compared with the if statement, for multi-condition judgment, the structure of switch is clear and the execution efficiency is high. The disadvantage is that the switch cannot judge the interval.