Take you to learn C step by step (second)

Catalog

One 、 Write a program

Two 、 data type

---

One 、 Write a program

C There must be only one main function in the code of language , namely main function

The standard format is as follows ：（ Other writing methods are not recommended ）

int main()
{

	return 0;
}

Note that all symbols are English characters .

What is a function ？

Let's briefly introduce some knowledge of functions ：

We can compare a function to a factory , When we have a need , For example, we want to drink coke , Then we need a soda factory , The factory goes through a series of processing , Finally, make coke and give it to us , Sometimes we need to provide some raw materials to the factory .

main Is the name of the function , It is equivalent to the name of the factory . Add a pair of brackets at the end () Indicates that it is a function , namely main() It means a function ;

int For integer , This means that the function will return an integer data after execution ; It's like the word "soda" in a soda factory , After working in the factory , It will produce soda for us .

{ } Represents the body of the function , The program will follow { } The statements in the are executed step by step ; This is equivalent to how to produce soda water inside the factory .

return 0; Is the statement at the end of the function , It means to return an integer number 0, With the beginning int echo . That is to say, the factory finished and returned the soda , If there is no such statement , It's equivalent to working in a factory but not giving you soda ！

Now just have a brief look , More on that later .

Next, we try to output something on the screen ：

#include <stdio.h>
int main()
{
	printf("Hello world!\n");
	return 0;
}

The result of the program execution is to print on the screen Hello world! And move the cursor to the next line , That is, I will change my line , Press ctrl + F5 Ready to run program .

Let's analyze this program again ：

First let's look at ,printf(); There is () prove printf It's a function , The function of this function is to print on the screen “ ” Contents of Li . It's like you go to a printing factory , You should give others the content to be printed . This content , Just put it in ( )  in . So where does this function come from ？

stay C In language , Using any function requires declaration 、 Definition . Some functions are universal , Classify them into files ,printf This function is put in stdio.h In this header file . Now let's go back to the first line ：

#include <stdio.h> Means to put the contents of this header file into this code . So we can use it printf Function ！

as for Hello world! hinder \n We'll talk about it later , Here we only know that it means line feed .

If your computer presses ctrl + F5 It doesn't work , Then try pressing ctrl + FN + F5; Or as shown in the figure below ：

Two 、 data type

To represent all kinds of data in life ,C Language provides three basic data types , Here's the picture ：

  So why do you put integer 、 Floating point types are divided into so many types ？

before this , We first need to know how much memory these types occupy , Although the above figure has been listed , But you can still verify it yourself ：

#include <stdio.h>
int main()
{
	printf("%d\n", sizeof(char));     //1
	printf("%d\n", sizeof(short));    //2
	printf("%d\n", sizeof(int));      //4
	printf("%d\n", sizeof(long));     //4
	printf("%d\n", sizeof(long long));//8
	printf("%d\n", sizeof(float));    //4
	printf("%d\n", sizeof(double));   //8

	return 0;
}

There's a little bit of caution here ：sizeof Although the following is added ( ) , But it's not a function , It's an operator , image + - * / The same operator .

sizeof You can calculate the size of its contents , Unit is byte . What is the concept of byte ？

The smallest unit in a computer is bit - bits , Only one can be stored 0/1;

byte - byte ,1 byte = 8 bit, Can express 0 - 2^8-1, namely 0-255 common 256 Number ;

1 kb = 2^10 byte;

1 mb = 2^10 kb;

1 gb = 2^10 mb;

1 tb = 2^10 gb;

1 pb = 2^10 tb;

% Is to format the output ,%d Is output in integer form .

When the types are rich enough , We can be more flexible when using , Increase memory utilization .

So how to use types ？

If I need to store a person's age  20; Then where to deposit ？ It must be memory , We need to apply for a space from the memory to store our data , The format is as follows ：

int age = 20;

Means to apply for a piece of memory int Type of space , I call this space age, What's in it is 20.

If you want to store a person's height 1.65, Namely double  high = 1.65;

All right. , This article ends here , If there are any questions , You can leave a message or a private message in the comment area , I promise I will read every one carefully , Reply earnestly . As for the more detailed content , such as floa t and double The difference between , We'll talk about it later , Now it's about putting C Know everything about language , Give you any code , You can understand .

The next article will talk about variables and constants .