Let the computer speak , Knowledge points （2-2） summary ：
* printf（" "）;
* printf—— Print "" Text in or letter
* there “\n” Indicates to let the cursor “ Line feed ”
* Its function is to make the computer “ suspend once ”
* This line of code causes the program to wait for keystrokes , The window closes after the user presses a key .
A little more colorful , Knowledge points （2-3） summary ：
How to set the background color and text color is , stay color Followed by two one digit numbers , The first number represents the background color , The second number indicates the text color . If in color after
Only one digit is added to the face , Indicates that only the text color is set , The background color still uses the default color . It should be noted that one digit here is actually 16 Hexadecimal , It can only be 0,1,
2,3,4,5,6,7,8,9,a,b,c,d,e,f One of .
for example ： system("color f5");
It should be noted that in color There should be a space after it
Digital color correspondence table ：
Let the computer add , Knowledge points （2-4） summary ：
* a = b;
* There is one here “=”, This is not equal to the sign , It's called the giving number （ also known as Assignment number ）, Similar to an arrow “←”, It means to put “=” The content on the right is assigned to “=” left .
* printf("%d", c);
* take “%d” Put between double quotation marks , Put the small house c Put it after double quotation marks , And separated by commas .
* At this time printf I found a in double quotation marks “ Debt collector ”, You know that you need to output a specific value at this time , Not symbols , The little house behind the double quotation marks c Ask for specific values .
* %d It's called a placeholder
Digital home —— variable , Knowledge points （2-5） summary ：
* int It's an English word integer（ integer ） Abbreviation of .
* We use float To apply for a small house , Used to store decimals , The form is as follows ：
* float a;
* be careful ： stay C In language , Decimals are called floating point numbers , use float express . Used before printf Statement output integer , Using “%d”. At this time, you need to output small data number , To use “%f”.
okay , Let's summarize , there “ Small house ” In us C In the terminology of language, it is called variable .int and float Explain what type of data is stored in a small house , here
Call it “ Variable type ” perhaps “ data type ”.
* similar int a; perhaps float a; Form of , We call it “ Define variables ”, Their syntax The format is as follows ：
* 【 term 】 Type of variable Name of the variable , Name of the variable ;
* 【 code 】 int a , b ;
* be careful ： If you give a small house many times a assignment , Small house a Will always be the most Last assigned value .
* This is because c Languages are executed sequentially , After executing one item, it will continue to execute the next item .
data output —— I'll do whatever I say , Knowledge points （2-6） summary ：
* printf Statement will only output the part inside the double quotation marks , The part outside the double quotation marks is only right The part within the double quotation marks serves as a supplementary explanation .
* for example ,printf（"%d+%d=%d", a, b, c）;
* Display one-to-one correspondence
data input —— What I say is what I say , Knowledge points （2-7） summary ：
* We need to read a number from the keyboard , Put it in a small house a in , The code is as follows ：
* scanf("%d", &a);
* “&” Symbols we call “ Fetch address character ”, abbreviation “ Addressing character ”. Its function is to get a small house a Address of .
* output a The value in does not require an address , And input needs
* For example ： If you want to go to a classroom , Then you need to know before class The address of this classroom , So you can go ; But if class is over , You need to get out of this
classroom , Because you are already in the classroom , So the address of this classroom is no longer needed .
How many kinds of small houses are there , Knowledge points （2-8） summary ：
* float and double All placeholders are %f, Can also be written as %.15f, there .15 Indicates that it is accurate to the decimal point 15 position
* Here's a special explanation , stay use scanf Read in double The placeholder used for data types is “%lf”（ Note that this is not a number 1 It's letters l） instead of “%f”.
* use char Small house applied for Is used to store characters . If you enter a string of characters, only the first character will be saved .
char The duty cycle of is %c
Logical challenge 1： Exchange numbers in small houses , Knowledge points （2-10） summary ：
* Now there are a=1,b=2, To exchange a,b Value of , Can't write directly
* A new register needs to be defined .
because c Language statements are executed anterograde .
* There's another one , No method to define new variables ：
scanf("%d%d", &a, &b); // a=1,b=3
printf("%d %d", a, b);
How to write comments ：
// or /* */