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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;
}

Run/Observe Results: During runtime, you need to input data as prompted, and the output will vary based on the input content and branch conditions.

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

Running/Observation Results: After running, the corresponding content will be printed according to the output statements. The variable values can be inferred based on the order of initialization, assignment, and function calls.

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

Run/Observe Results: During runtime, you need to input data as prompted, and the output will vary based on the input content and branch conditions.

  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

Running/Observation Results: After running, the corresponding content will be printed according to the output statements. The variable values can be inferred based on the order of initialization, assignment, and function calls.

cin is used with the stream extraction operator >>

std::cin >> a     //输入一个变量a

Run/Observe Results: During runtime, you need to input data as prompted, and the output will vary based on the input content and branch conditions.

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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