CPP

Lecture 3 : Input-Output

Output Instruction

• In C, standard output device is monitor and printf() is used to send data/message to monitor
• printf() is a predefined function.
• In C++, we can use cout to send data/ message to monitor.
• cout is a predefined object
• The operator « is called insertion or put to operator

printf("Hello World!"); //in C
cout << "Hello World!"; // in C++

printf("sum of %d and %d is %d", a,b,c);
cout << "sum of "<<a<<" and "<<b<< "is" << c;

printf("%d", a+b);
cout << a+b;

Input Instruction

• In C, Standard input device is keyboard and scanf() is used to recieve data from keyboard.
• scanf() is a predefined function.
• In C++, we can use cin to input data from keyboard.
• The identifier cin is a predefined object in C++.
• The operator » is known as extraction or get from operator

scanf("%d", &a); // in C
cin >> a; // in C++

scanf("%d%d",&a, &b);
cin >> a >> b;

Remember

• According to the ANSI standards for C language, explicit declaration of function is recommended but not mandatory.
• ANSI standards for C++ language says explicit declaration of function is compulsory.

Header files

• predefined functions are declared in header files, so whenever you are using any predefined function in your code, you have to include specific header file that contains its declaration.

About iostream.h

• We need to include header file iostream.h, it contains declarations for the identifier cout and the operator «. And also for the identifier cout and operator ».
• Header file contains declaration of identifiers.
• Identifiers can be function names, variables, objects, Macros, etc.

endl

• Inserting endl into the output stream causes the screen cursor to move to the beginning of the next line.
• endl is a manipulator and it is declared in iostream.h
• ‘\n’ character also works as it works in C.

Sample Program (square.cpp)

#include <iostream.h> //Declaration of cin and cout
#include <conio.h> //Declaration of clrscr(), getch()

//action statements
int main()
{
	clrscr();
	int x; //Declaration after action statement
	cout << "Enter a Number : " << endl;
	cin >> x;
	int s = x*x; //Run-time / Dynamic Initializaton
	cout << "Square of" << x << "is" << s;
	return 0;
}