The so-called declaration (Declaration) is to tell the compiler that I want to use this function. It doesn’t matter if you don’t find its definition now. Please don’t report an error. I will fill in the definition later.
The format of function declaration is very simple, which is equivalent to removing the function body in the function definition and adding a semicolon; at the end, as shown below:
dataType functionName( dataType1 param1, dataType2 param2 ... );
You can also write no formal parameters, Write-only data type:
dataType functionName( dataType1, dataType2 ... );
The function declaration gives the function name, return value type, parameter list (emphasis on parameter type) and other information related to the function, which is called the function prototype (Function Prototype).
The function prototype is to tell the compiler information related to the function, so that the compiler knows the existence of the function and its existing form. Even if the function is not defined temporarily, the compiler knows how to use it.
Example:
#include <stdio.h> //函数声明 int sum(int m, int n); //也可以写作int sum(int, int); int main(){ int begin = 5, end = 86; int result = sum(begin, end); printf("The sum from %d to %d is %d\n", begin, end, result); return 0; } //函数定义 int sum(int m, int n){ int i, sum=0; for(i=m; i<=n; i++){ sum+=i; } return sum; }
Recommended: "c Language Tutorial"
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C# is a programming language, while .NET is a software framework. 1.C# is developed by Microsoft and is suitable for multi-platform development. 2..NET provides class libraries and runtime environments, and supports multilingual. The two work together to build modern applications.

C#.NET is a powerful development platform that combines the advantages of the C# language and .NET framework. 1) It is widely used in enterprise applications, web development, game development and mobile application development. 2) C# code is compiled into an intermediate language and is executed by the .NET runtime environment, supporting garbage collection, type safety and LINQ queries. 3) Examples of usage include basic console output and advanced LINQ queries. 4) Common errors such as empty references and type conversion errors can be solved through debuggers and logging. 5) Performance optimization suggestions include asynchronous programming and optimization of LINQ queries. 6) Despite the competition, C#.NET maintains its important position through continuous innovation.

The future trends of C#.NET are mainly focused on three aspects: cloud computing, microservices, AI and machine learning integration, and cross-platform development. 1) Cloud computing and microservices: C#.NET optimizes cloud environment performance through the Azure platform and supports the construction of an efficient microservice architecture. 2) Integration of AI and machine learning: With the help of the ML.NET library, C# developers can embed machine learning models in their applications to promote the development of intelligent applications. 3) Cross-platform development: Through .NETCore and .NET5, C# applications can run on Windows, Linux and macOS, expanding the deployment scope.

The latest developments and best practices in C#.NET development include: 1. Asynchronous programming improves application responsiveness, and simplifies non-blocking code using async and await keywords; 2. LINQ provides powerful query functions, efficiently manipulating data through delayed execution and expression trees; 3. Performance optimization suggestions include using asynchronous programming, optimizing LINQ queries, rationally managing memory, improving code readability and maintenance, and writing unit tests.

How to build applications using .NET? Building applications using .NET can be achieved through the following steps: 1) Understand the basics of .NET, including C# language and cross-platform development support; 2) Learn core concepts such as components and working principles of the .NET ecosystem; 3) Master basic and advanced usage, from simple console applications to complex WebAPIs and database operations; 4) Be familiar with common errors and debugging techniques, such as configuration and database connection issues; 5) Application performance optimization and best practices, such as asynchronous programming and caching.

C# is widely used in enterprise-level applications, game development, mobile applications and web development. 1) In enterprise-level applications, C# is often used for ASP.NETCore to develop WebAPI. 2) In game development, C# is combined with the Unity engine to realize role control and other functions. 3) C# supports polymorphism and asynchronous programming to improve code flexibility and application performance.

C# and .NET are suitable for web, desktop and mobile development. 1) In web development, ASP.NETCore supports cross-platform development. 2) Desktop development uses WPF and WinForms, which are suitable for different needs. 3) Mobile development realizes cross-platform applications through Xamarin.

The C#.NET ecosystem provides rich frameworks and libraries to help developers build applications efficiently. 1.ASP.NETCore is used to build high-performance web applications, 2.EntityFrameworkCore is used for database operations. By understanding the use and best practices of these tools, developers can improve the quality and performance of their applications.


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