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This article mainly introduces the relevant knowledge of C language function use case analysis, the content is detailed and easy to understand, the operation is simple and fast, and has a certain reference value. I believe you will gain something after reading this C language function use case analysis article. Let's take a look.

Function declaration and definition function declaration

Tell the compiler what a function is called, what the arguments are, and what the return type is. But the function declaration can't decide whether it exists or not.

The declaration of a function usually occurs before the use of the function. To meet the requirements of declaration before use

The declaration of the function is usually placed in the header file

Function definition

The definition of a function refers to the concrete implementation of the function and the functional realization of the function.

Give an example of a simple summation function

Generally write a simple summation function, the summation function is written directly in the main () function.

/ / simple summation function int main () {int a = 10; int b = 20; int sum = aquib; printf ("% d\ n", sum); return 0;} rewrite addition into a function separately

Write the addition function as a separate function and put it in front of the main function. If you put the function add after the main function, it will report an error, because the program is carried out from top to bottom, and after the main function is executed, it is found that the add function is undefined and cannot be found.

/ / there was a function before. Function is preceded by int add (int x, int y) {return x + y;} int main () {int a = 10; int b = 20; int sum = add (a, b); printf ("% d\ n", sum); return 0;} add function declaration int add (int x, int y); / / function declaration int main () {int a = 10 Int b = 20; int sum = add (a, b); printf ("% d\ n", sum); return 0;} int add (int x, int y) / / definition is placed after the main function, you need to declare {return x + y;} leading file and function declaration first

In fact, when there are many function codes, modular programming is generally adopted, and the function of each function is as simple as possible, with low coupling and high cohesion between functions. Therefore, for the addition function of the addition order above, rewrite it with the lead file.

Define the source file test.c, source file add.c, and header file add.h first

/ / Source file test. C#include "add.h" int main () {int a = 10; int b = 20; int sum = add (a, b); printf ("% d\ n", sum); return 0;} / Source file add.cint add (int x, int y) / / definition is placed after the main function, you need to declare {return x + y;} / header file add.hint add (int x, int y) / / declaration of function generation of static library (.lib)

When the programmer writes a subtraction function for others to use, but does not want to share the source code directly with others, the code can be compiled into a static library (that is, .lib files).

The characteristics of static library: compile the function into static library, others can use the encapsulated code normally, but can not see the source code.

Here is an example of how to generate a static library (.lib):

Create a new VS project, create a new source file sub.c and header file sub.h, and write a subtraction function sub

/ / Source file sub.cint sub (int x, int y) / / function definition needs to declare {return y-x;} / header file sub.hint sub (int x, int y)

Click solution Explorer-Project name-right-click Properties to bring up the dialog box.

Then click-- configure Properties-- General-- Project defaults-- configuration Type-- drop-down menu and select static Library (.lib)-- apply-- OK.

Then click generate-generate solution.

You will eventually see the static library .lib file in the Debug folder under the project folder.

Open the static library with notepad and you can see that it is garbled.

How to use static Library Files

Next, we show how to use static library files generated by others or by yourself:

(1) copy the function corresponding header file .h file and static library .lib to your own project file.

(2) add the t header file sub0119.h to the header file

(3) add subtraction header file reference and static library reference to the source file

# include "add.h" / / addition header file # include "sub0119.h" / / subtraction header file # pragma comment (lib, "sub0119.lib") / / static library must be added

(4) when the program is running, the generated static library will be loaded through the above reference. Use the subtraction function sub directly in the main function.

/ / lead file int main () {int a = 10; int b = 20; int sum = add (a, b); / / General function call int subnum = sub (a, b); / / use static library printf ("% d\ n", sum); printf ("% d\ n", subnum); return 0;}

The running program is shown in the following figure:

Function recursion what is recursion?

As an algorithm, recursion is widely used in programming languages.

A method in which a procedure or function calls itself directly or indirectly in its definition or description.

It usually transforms a large and complex problem into a smaller problem similar to the original problem to solve.

Only a small number of programs are needed to describe the repeated calculations needed in the problem-solving process, which greatly reduces the amount of code of the program.

The main way of thinking of recursion is to reduce the big things into small ones and turn the problems into small problems that can be repeated a limited number of times.

Two necessary conditions for Recursion

There is a restriction, and when this restriction is met, the recursion will not continue.

It is getting closer and closer to this restriction after each recursive call.

Exercise 1

Accept an integer value (unsigned) and print each bit in order.

Input: 1234, output 1234

General method void print (num) / / Custom print function {int arr [10] = {0}; / / define array for (int I = 0; I

= 0; iMel -) {/ / print printf backwards ("% d", arr [I]);}} int main () {int num = 1234; print (num); return 0;} recursive method

Analysis: print 1234 can be disassembled as shown below, taking out the numbers on different bits, and finally disassembling the numbers to the last bit, start printing:

Print (1234), a number greater than 9 indicates that the number is not yet a single digit, so 1234 is split into 123and 4, respectively, by taking the remainder and taking the module. Pass the remaining 123 to the function print again

Print (123). A number greater than 9 indicates that the number is not yet a single digit, so 123 is disassembled into 12 and 3, and the remaining 12 is passed to the function print again by taking remainder and module operation, respectively.

Print (12), the number greater than 9 indicates that the number is not yet a single digit, so the 12 is disassembled into 1 and 2, and the remaining 1 is passed to the function print again through the remainder and module operation, respectively.

Print (1), the number less than 9 indicates that the number is a single digit, that is, it is decomposed to the last step, which is the limitation of recursion, so the 1 module operation is printed out.

The code is as follows:

Void print (int num) {if (num > 9) {print (num/10); / / take the remainder} printf ("% d", num% 10); / / take the module} int main () {int num = 1234; print (num); return 0;}

Through debugging, we analyze the running logic of the entire recursive program as shown in the following figure. The red circle 1, 2, 3, 4 indicates the execution order of the program:

The first time to call the function print, when num=1234, n > 9, satisfies the if condition, executes print (123), and calls the function print itself.

The second call to the function print, when num=123, n > 9, satisfies the if condition, executes print (12), and calls the function print itself.

The third call to the function print, when num=12, n > 9, satisfies the if condition, executes print (1), and calls the function print itself.

When the function print is called for the fourth time, num=1, n

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