C Language Study Notes (1) -- C Language

 

I have been using java for a long time. Now I am very happy to learn the C language and expand my career.

 

1. The first c program:

 

 

 

# Include "stdio. h"/* this line is the file inclusion command */

Main (){

Printf ("test");/* function call: printf outputs the content to the display */

}

Note: The C language is case sensitive;

 

The program must contain one primary function with only one name as main;

 

Each program line must end;

 

/*... */Is the comment content.

 

 

2. Example: calculate the area and perimeter of any radius circle.

 

# Include "stdio. h"

Main (){

Float r, l, area;/* defines the float Type Variable */

Scanf ("% f", & r);/* call the keyboard input function */

L = 2*3.14 * r;

Area = 3.14 * r;

Printf ("\ n l = % f, area = % f \ n", l, area );

}

Note: r, l, and area are float variables that can be changed during the program running. float is a data type in C.

 

3. Calculate the sum of two numbers.

 

# Include "stdio. h"

Main (){

Int I, j, sum;

Int Add (int m, int n);/* declare a function */

Scanf ("% d", & I, & j );

Sum = Add (I, j);/* call the function */

Printf ("\ n sum = % d \ n", sum );

}

Int Add (int m, int n) {/* function */

Return m + n;

}

Note: The & operator in scanf ("% d", & I, & j); is the get address operator.

 

Summary of the above three examples:

 

1. a c-language source program can be composed of one or more source files. Each source file can be composed of one or more functions. A source program can contain no matter how many source files or functions, you can only have one and only one mian function.

 

The Instruction introduced by "#" is a preprocessing instruction.

 

4. common syntax specifications.

Identifier: variables, function names, and labels in the program are collectively referred to as the identifier. The C language specifies that the identifier can only contain letters, numbers, and underscores (_). The first character must be a letter or underscore.

 

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