[C++] Chapter1. Introduction to Computers, Programs, and C++

• Simple comsole output

#include <iostream>

using namespace std;
int main()
{
	cout << "Welcome to C++!" << endl;
	return 0;
}

-> #include : compiler preprocessor directive [컴파일러 전처리 지시자]

-> iostream : standard input output header file

-> cout : is same printf of C

 

• cout and << operator
  • cout
    • console output
    • standard C++ output stream object
    •  
  • << operator
    • stream insertion operator
    • multiple object value operator [C와는 다른점]

• cin, cout defined in iostream header
• namespace [이름공간]
  • Name(identifier) conflicts
  • namespace keyword
    • name conflict resolution [이름충돌 해결]
    • Names declared in a namespace are separate from other namespaces
  • using name space std;
    • cout and cin are defined in the iostream library in the std namespace
  • std::
    • one of the namespeaces defined by the ANSI  C++ standard
    • std:: prefix [접두사]
      • std::cout, std::cin, std::endl
    • can omit std::
      • "using namespace std"ons 
• computing with numbers
  • mathematical computations and displays the result to the console

#include <iostream>
using namespace std;
int main()
{
	cout << "(10.5+2*3) / (45-3.5)=";
	cout << (10.5 + 2 * 3) / (45 - 3.5) << endl;

	return 0;
}

 

• Programming Errors
  • syntax errors
    • Missing braces : { }
    • Missing Semicolons : ;
    • Missing Quotation Marks : " "
    • Misspelling Names : Name conflicts
  • runtime errors
    • impossible syntax like division '0'
  • logic errors
    • loop forever [condition not set]

#include <iostream>
using namespace std;
//prototype of area 
double  area(int r);

int main_intheclass()
{

	int n = 3;
	//cout the return value from area () which calculates area of a circle
	cout << area(n);

	char c = '#';
	cout << c << 5.5 << '-' << n << "hello" << endl;
	cout << "n + 5 = " << n + 5 << endl;

	return 0; // OS로 보낸다
}

double  area(int r)
{
	double ret = 3.14159 * r * r; //double r로 지정하면 안된다.
	return ret; // return r로 하면 안된다.
}