Setting out to C++

C++ Initiation

• Comments, indicated by the // prefix
  • C: /* comments */
  • Pascal: (* comments *)
  • Modula-2: (* comments *)
  • Basic: REM comments
  • Fortran: (1st position)* comments
  • Cobol: (7th position)* comments
  • Ada: -- comments
• A preprocessor #include directive
  • C: #include
    Pascal: (input, output)

    Modula-2: IMPORT IO;

    Basic: include filename

    Fortran: No preprocessor

    Cobol: No preprocessor (ENVIRONMENT DIVISION)

    Ada: with TEXT_IO;
• A function heading: int main(void)
  • C: int main(void)
  • Pascal: PROGRAM Pname()
  • Modula-2: MODULE Mname;
  • Basic: REM comments
  • Fortran: FUNCTION Fname()
  • Cobol: PROCEDURE DIVISION
  • Ada: PROCEDURE Pname IS
• A function body, delimited by { and }
  • C: { and }
  • Pascal: BEGIN and END.
  • Modula-2: BEGIN and END Mname.
  • Basic: SUB Sname and END SUB
  • Fortran: FUNCTION Name and END
  • Cobol: 01 02 03 blocks
  • Ada: BEGIN and END;
• A statement using the C++ cout facility to display a message
  • C: printf("This is C message\n")
  • Pascal: Writeln("This is Pascal message")
  • Modula-2: IO.StringOut(This is Modula-2 message")
  • Basic: PRINT "This is a Basic message"
  • Fortran: PRINT *, "This is a Fortran message"
  • Cobol: WRITE record-name
  • Ada: Simple_IO.Write("This is a Ada message ")
• A return statement to terminate the main() function
  • C: return
  • Pascal: END.
  • Modula-2: END Mname.
  • Basic: END
  • Fortran: END
  • Cobol: .
  • Ada: END Pname;

// myfirst.cpp--displays a message

#include <iostream.h>	// a PREPROCESSOR directive
int main(void)	// heading summarizes 
		// function
{		// start of function body
	cout << "Come up and C++ me some time.";	// message 
	cout << "\n";	// start a new line
	return 0;	// terminate main()
}		// end of function body

More About C++ Statements

• Declaration statement announce the name and the kind of variables used in a function.
• Assignment statements use the assignment operator (=) to assign a value to a variable.
• Function calls activate a function. When the called function terminates, the program returns to the statement in the calling function immediately following the function call.
• Message statements send a message to an object, initiating some sort of action.

// fleas.cpp -- display the value of a variable

#include <iostream.h>
int main(void)
{
	int fleas;       // create an integer variable
	fleas = 28;       // give a value to the variable
	cout << "My cat has ";
	cout << fleas;		// display the value of fleas
	cout << " fleas.\n";
  	return 0;
}



// yourcat.cpp -- input and output

#include <iostream.h>
#include <stdio.h>	// used for old C I/O functions
int main(void)
{
	int fleas;

	puts("How many fleas does your cat have?");	// Old C
	cin >> fleas;					// C++ input
// next line concatenates output
	cout << "Well, that's " << fleas << " fleas too many.\n";
	return 0;
}

Functions

• Using Library Functions: include the function header file which has the prototype in it. Example: iostream.h math.h
• User-defined functions: type the function prototype into your source file or include a user-defined header file.
• General functional features:
  • It has a heading and a body
  • It accepts an argument
  • It returns a value
  • It requires a prototype

---

// sqrt.cpp -- use a square root function

#include <iostream.h>
#include <math.h>     		// use with math functions
int main(void)
{
	double cover;     			// use double for real numbers

	cout << "How many square feet of sheets do you have?\n";
	cin >> cover;
	double side;		// create another variable
	side = sqrt(cover);	// call function, assign return value
	cout << "You can cover a square with sides of " << side;
	cout << " feet\nwith your sheets.\n";
	return 0;
}



// ourfunc.cpp -- defining your own function

#include <iostream.h>
void simon(int);	// function prototype for simon()
int main(void)
{
simon(3);	// call the simon() function
cout << "Pick an integer: ";
int count;
cin >> count;
simon(count);	// call it again
return 0;
}

void simon(int n)	// define the simon() function
{
cout << "Simon says touch your toes " << n << " times.\n";
}							
	// void functions don't need return



// convert.cpp -- converts stone to pounds

#include <iostream.h> 
int stonetolb(int); 	// function prototype 
int main(void) 
{
	int stone; 
	cout << "Enter the weight in stone: "; 
	cin >> stone; 
	int pounds = stonetolb(stone); 
	cout << stone << " stone are "; 
	cout << pounds << " pounds.\n"; 
	return 0;
}

int stonetolb(int sts) 
{
	return 14 * sts; 
}