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preface
1, What is C language?
C language is a language Process oriented of Abstraction General programming language, widely used in Bottom development . C language can be written in a simple way compile . low level processing storage . C language produces only a small amount of machine language And don't need any Operating environment Support an efficient programming language that can run. Although C language provides many low-level processing function , but it still remains Cross platform C language programs written in a standard specification can include similar features Embedded processor as well as Supercomputer And many other operating platforms Computer platform Proceed on compile.
2, The first C language program
Welcome to the world of programming, petite little princess (Prince)!
#include <stdio.h>
int main()
{
printf("hello world\n");
return 0;
}
//The main function is the entry of the program
//There is only one main function in a projectII. Data type
Mastering data types is a necessary way to learn C language.
char //Character data type short //Short int //plastic long //Long integer long long //Longer shaping float //Single-precision floating-point double //Double precision floating point number
#include <stdio.h>
int main()
{
printf("%d\n", sizeof(char));
return 0;
}
//By analogy, you can try other data types
//In programming software, sizeof (long) > = sizeof (int)
//sizeof() is a memory capacity measurement function that returns the size of a variable or type (in bytes); In C language, sizeof() is an operator to judge the data type or expression length. You can try it on the computer.char ch = 'w'; int long= 120; float width = 200f;
III. constants and variables
3.1 interpretation of terms
Some values in life are constant (such as pi, gender, ID number, blood type, etc.) - variables.
Some values are variable (e.g. age, weight, salary) - variables
3.1} classification of variables (local variables and all variables)
The following is a brief code introduction
#include <stdio.h>
int A = 2019;//global variable
int main()
{
int B = 2018;//local variable
int A = 2020;//local variable
printf("A = %d\n", A);
return 0;
}
//There is no problem with the definition of local variable A above!
//When local variables and global variables appear at the same time, local variables are used first3.2 scope and life cycle of variables
Scope
life cycle
3.3 constants
#include <stdio.h>
//give an example
//Ale, female and secret in parentheses are enumeration constants
enum Sex
{
MALE, // 0
FEMALE, // 1
SECRET // 2
};
//Note: enumeration constants start from 0 by default and increase by 1 in turn
int main()
{
//Literal constant presentation
3.14159;//Literal constant
2000;//Literal constant
//const modified constant
const float Pai = 3.14f; //Pai here is a constant variable modified by const
Pai = 6.33;//It cannot be modified directly!
//#Demonstration of identifier constant of define
#define MAX 100
printf("max = %d\n", MAX);
//Enumeration constant demo
printf("%d\n", MALE);
printf("%d\n", FEMALE);
printf("%d\n", SECRET);
return 0;
}summary
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