C + + Basic 1 data type constant

Keywords: C++ string

Using Dev CPP as the programming environment

Note that dev cpp5.4.0 does not have the function of formatting code, so do not set it again
Set common shortcuts for
Ctr+E: multiline comment
Ctrl+Shift+E: uncomment multiline

Ctrl+Z: undo
Ctrl+Shift+Z: cancel undo

Ctrl+L: collapse function
Ctrl+Shif+L: unfold function

Set Dev Cpp

Dev C + + initialization (default) code modification method

C + + Basics

C + + is a static, compiled, general, case sensitive and irregular programming language. It supports procedural programming, object-oriented programming and generic programming. [object oriented and process oriented]

C + + is considered as an intermediate language, which combines the characteristics of high-level language and low-level language.

C + + is a superset of C. in fact, any legal C program is a legal C + + program.

The first C + + program

Starting with # tells the compiler that this line of code needs preprocessing. include tells the compiler that the header file iostream needs to be introduced. The iostream file defines the input / output stream objects.

using namespace std;// Use a namespace named STD, which contains the functions of the C + + standard library.

Cout < < "Hello World!" is used to output "Hello World!" to the screen.

return is the last instruction statement in the program. It terminates the main() function and returns 0 to the calling process. A non-zero value (usually 1) indicates abnormal termination.

The cout operator does not insert a newline character at the end, so if you want to print two lines, you can use the endl manipulator; Endl is only a way of line feed operation. We can also use the escape character "\ n" for line feed

#include<iostream>
#include<stdio.h>
#include<stdlib.h>
using namespace std;
int main()
{
	//#include<stdlib.h> 
	cout<<"hello world"<<endl;
	//#Include < stdlib. H > standard library 
    system("pause");
    return 0;
}



Framework of C + + program


Keywords, identifiers, constants


C + + identifier:
Starts with a letter or underscore and contains numbers, letters, and underscores

keyword

C + + compilation process

Edit hello.cpp – > compile hello.obj – > link (project. exe) - > run (run. exe file)
Note. cpp is the source code of C + +, and. C is the source code of C language

Single line and multiline notes

Comments are explanatory statements that can be included in C + + code to explain the functions of the code.
The compiler ignores everything that appears in the comment, so no information is displayed in the result.

Single line note:
Comments that begin with two slashes (/ /) are called single line comments. Slashes tell the compiler to ignore everything that follows until the end of the line.

Multiline comment:
Multiline comments start with * * / * * * and end with * * * / * *. You can put them on the same line or insert one or more lines of code between them.

C + + programming summary

variable and constant

Literal constant and Symbolic Constant

Literal constants: integer constants


Octal and hexadecimal in C + + will be converted to decimal output

Literal constants: real constants


cout in C + + outputs six significant digits by default. If it exceeds 6 digits, it will be rounded to output six digits
C language:
float-4byte - keep 6 decimal places - add f or F when using
double-8byte-15 decimal places reserved

The output decimal 37.0 will output integer by default: 37
Scientific counting method:
1.2E-38=1.2*10^-38
Index bit: - 38
Mantissa: decimal

5.12e2=5.1210^2=512
5.12E2=5.1210^2=512
Dev Cpp output: 1.2e+002 means 1.2 * 10 ^ 2
+Or - 002: positive or negative

Case:

#include<iostream>
#include<iomanip>
#include<stdio.h>
using namespace std;
int main()
{
	// 67: decimal 077: octal 0x78: hexadecimal 
	cout<<67<<"\t"<<077<<"\t"<<0x78<<"\n"<<endl; 
	//Output: 67 63 120
	
		
	//General form
	cout<<11<<"\t"<<0.12<<"\t"<<-9.8<<"\t"<<.9<<"\t"<<-39.<<"\n"<<endl; 
	//Output: 11 0.12 - 9.8 0.9 - 39
	
	
	 
	//Note: cout in C + + outputs six significant digits by default. If it exceeds 6 digits, it will be rounded to output six digits
	cout<<7.793456<<"\n"<<endl; //7.79346
	//The output of C is simpler 
	printf("%.4f\n",234.4678);//234.4678
	
	//Note: the output decimal 37.0 will output integer 37 by default
	cout<<37.0<<"\n"<<endl;//37

	//Scientific counting method: setprecision(n): note that after setting it once, the subsequent output will be limited to 2 significant digits 
	cout<< setprecision(2)<<123.444546<<"\n"<<endl;//1.2e+002


	return 0;
}

Text constant: character constant


Escape character


Difference between string constant and character constant:

 //c + + string
string x="xwer";

\Is an escape character. If it is followed by a number, it represents the character corresponding to the ASCII value. The number here is usually a 1-3-digit octal number, and it can also be represented by hexadecimal in the form of \ xNN.
For example '\ 141': the ASCII code representing \ 0141 octal 141 is' a '

Case:

//auther:dq
//function: literal constant: integer constant real constant character constant string constant 2
#include<iostream>
#include<stdio.h>
using namespace std;

int main() {
	//'a': character 'aa': a string consisting of two 'a' and string end tag '\ 0' 
	cout<<'a'<<"\t"<<"aa"<<"\n"<<endl; 
	
	
	//\Is an escape character. If it is followed by a number, it represents the character corresponding to the ASCII value
	//The numbers here are usually 1-3-digit octal numbers, which can also be expressed in hexadecimal in the form of \ xNN.
    //For example '\ 141': the ASCII code representing \ 0141 octal 141 is' a '
	 cout<<0141<<"\t"<<'\141'<<"\t"<<'\061'<<"\n"<<endl;//97      a       1
	 cout<<0x60<<"\t"<<'\x60'<<"\n"<<endl;//96      `
	 
	 //c + + string
	 string x="xwer";
	 cout<<x<<endl; 
	 	 
	 return 0; 
}

Symbolic constants: identifier constants




Case:

//auther:dq
//function: symbol constant: identifier constant const 
#include<iostream>
#include<iomanip>
using namespace std;
int main()
{
	const char x='a';
	const int y=8;
	const double z=8.2345;
	
	cout<<x<<"\t"<<y<<"\t"<<fixed<<setprecision(2)<<z<<"\n"<<endl;
	 
	return 0;
}

Constant summary

Memory addressing



Basic data type

bool char 1 1
short int long 2 4 4
float double long double 4 8 8


Case: output the value of x+y

//Header file 
#include<iostream>
#include<stdio.h>
#include<stdlib.h>
// Namespace identifier 
using namespace std;
//Main function 
int main()
{
	//Declarative variable 
	int x,y,z;
	//Variable assignment 
	x=1;
	y=9;
	z=x+y;
	//cout: output stream object < <: output stream operator 
	cout<<"The result is:"<<"\n"; 
	cout<<"x+y="<<z<<endl;
	return 0;

}
 
 

Summary of variables

Input stream and output stream Cin Cout

CIN > > r: enter a value from the keyboard to r
Cout < < R: output r to the screen
Note: when writing a floating point constant, add a decimal point

    double r;
	cout<<"input:r"<<endl;//Prompt statement 
	cin>>r;
    cout<<"r="<<r<<endl;

Keep several significant digits

setprecision(n): n significant digits are reserved

//Scientific counting method: setprecision(n): note that after setting it once, the subsequent output will be limited to n significant digits 
cout<< setprecision(2)<<123.444546<<"\n"<<endl;//1.2e+002

123.444546 exceeds 2 digits, and the decimal point moves to the left until it is 2 digits
Move right: + 002

Keep several decimal places

Fixed < < setprecision (n): keep N decimal places

	#include<iomanip>
 	cout<<fixed<<setprecision(2)<<s<<endl; 

Case: finding the area of a circle




#include <iostream>
#include<iomanip>
using namespace std;
void circle(double r)
{
	double pi=3.1415;
	double s=pi*r*r;
	double c=pi*2.0*r; 
	cout<<"s="<<s<<"\n"<<"c="<<c<<endl; 
	//cout<<"s="<<fixed<<setprecision(2)<<s; Keep two digits after the decimal point
	cout<<"s="<<fixed<<setprecision(4)<<s<<"\n"<<"c="<<fixed<<setprecision(4)<<c<<"\n"<<endl;

	
}

int main()
{
	double r;
	cout<<"input:r"<<endl;//Prompt statement 
	cin>>r;
	circle(r);
    cout<<"end"<<endl;
    return 0;
}

Posted by NoFear on Sun, 24 Oct 2021 10:42:08 -0700