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Input and Output

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Input and Output

Data input

Function: Used to get data from the keyboard

Keywords: cin

How to Write Your First Program Using the 8051 Microcontroller

This is a tutorial on using the 8051 microcontroller for programming. Here, I will guide you through how to write your first program. In the tutorial, I will explain how to set up the environment and how to run programs on the 8051 microcontroller.

8051 Microcontroller Tutorial

  • 8051 Microcontroller Introduction
  • 8051 Microcontroller Environment Setup
  • How to Program the 8051 Microcontroller

References

Syntax: cin >> 变量

Example:

int main(){

    //整型输入
    int a = 0;
    cout << "请输入整型变量：" << endl;
    cin >> a;
    cout << a << endl;

    //浮点型输入
    double d = 0;
    cout << "请输入浮点型变量：" << endl;
    cin >> d;
    cout << d << endl;

    //字符型输入
    char ch = 0;
    cout << "请输入字符型变量：" << endl;
    cin >> ch;
    cout << ch << endl;

    //字符串型输入
    string str;
    cout << "请输入字符串型变量：" << endl;
    cin >> str;
    cout << str << endl;

    //布尔类型输入
    bool flag = true;
    cout << "请输入布尔型变量：" << endl;
    cin >> flag;
    cout << flag << endl;
    return EXIT_SUCCESS;
}

运行结果（以下为按提示依次输入 10、20、30……时的一次示例）：

请输入整型变量：
10
请输入浮点型变量：
20
请输入字符型变量：
3
请输入字符串型变量：
0
请输入布尔型变量：
1

C-style I/O and C++ stream I/O

  1. scanf and printf in C's stdio.h

The int scanf(const char *format, ...) function reads input from the standard input stream stdin and scans the input according to the provided format.

The int printf(const char *format, ...) function writes output to the standard output stream stdout and produces output according to the provided format.

printf("输出内容(可含占位符)"，变量1，变量2)

printf("%d",a);      //输出一个整形变量a
printf("%f %f",a,b);   //输出二个单精度浮点数变量(fp32) a，b中间以空格隔开
printf("%d序号对应的值是%lf",a,b);   //输出二个单精度浮点数变量a，b中间以空格隔开
printf("%.2f",a);   //输出一个单精度浮点数(fp32) a,并保留两位小数
printf("你好")  //输出“你好”字符串

运行结果： 此代码块不含 main 函数，是语法、接口或分文件示例，不能独立运行，因此没有终端输出。

scanf("%d",&a);           //输入一个整形数
scanf("%d %d",&a，&b);   //输入两个整形数，中间以空格隔开      
scanf("%d,%d",&a，&b);   //输入两个整形数，中间以逗号隔开

运行结果： 此代码块不含 main 函数，是语法、接口或分文件示例，不能独立运行，因此没有终端输出。

  1. std::cin and std::cout in C++'s iostream

cout is used in conjunction with the stream insertion operator <<.

std::cout << a;   //输出一个变量a
std::cout << "你好"   //输出"你好"
std::cout << "结果是：" << a << std::endl  //输出 结果是: a  并换行

运行结果： 此代码块不含 main 函数，是语法、接口或分文件示例，不能独立运行，因此没有终端输出。

cin is used with the stream extraction operator >>

std::cin >> a     //输入一个变量a

运行结果： 此代码块不含 main 函数，是语法、接口或分文件示例，不能独立运行，因此没有终端输出。

Modern C++ Formatted Output

The previously introduced printf and std::cout are both very commonly used, but each has its drawbacks: printf is less type-safe when its format placeholders are written incorrectly, while std::cout can be verbose when outputting multiple variables consecutively.

Modern C++ provides more suitable tools for formatted output:

  • std::format (C++20): generates formatted std::string, with concise syntax and type safety.
  • std::print / std::println (C++23): Directly formatted output, println automatically wraps.

For example, when outputting a name and score, std::cout is often written as std::cout << name << ": " << score << std::endl;, and modern writing can be written as std::println("{}: {}", name, score);.

std::print / std::println by default outputs to standard output, but the first parameter can also be set to stdout or stderr. Here, stdout / stderr refer to the C standard library's FILE*, not std::cout.

The later section on modern C++ will cover in detail: std::format / std::print.

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