Getting Started in C++

Tom Kelliher, CS17

Feb. 21, 1996

Your First Program

/**********************************************************************
 * convert.cc
 * Tom Kelliher
 * CS18, Feb. 21, 1996
 * 
 * This program will prompt for a temperature in degrees Fahrenheit,
 * convert it to degrees Celsius, and output the converted temperature.
 * Input from the keyboard
 * Output to the console
 **********************************************************************/

// Preprocessor directives:
#include <iostream.h>

// Named constant definitions:
const float FRACTION = 5.0 / 9.0;

// Main program:

int main()
{
   float fahrenheit;   // fahrenheit temperature
   float celsius;      // celsius temperature
   
   // program statements follow
   cout << "Please enter a temperature in degrees Fahrenheit: ";
   cin >> fahrenheit;
   
   celsius = FRACTION * (fahrenheit - 32.0);
   
   cout << "That is " << celsius << " degrees Celsius" << endl;
}

Program Elements

Comments

• Purpose
• Two forms:
  • /* */
  • //

Preprocessor Directives

• Relationship to compiler
• Begin with #
• Header files:
  • #include <iostream.h>
  • #include "myheader.h"
• No ;

Data Types and Type Declarations

Data type:

a set of data values and a set of operations on those values.

Examples:

int counter;
char more;
float size;
double distance;

Characteristics:

• Amount of RAM, how stored
• Valid operations
• Meaning of operations: 5/9 vs. 5.0/9.0

Fundamental vs. derived types

Some fundamental types:

• char
• int --- small range on PC
• double

Initialization in declaration:

int size = 10;
char more = 'y';
double fahrenheit = 1.23E9;

Named Constants

A ``variable'' with unchanging value:

const double PI = 3.14159;
const int FEET_PER_MILE = 5280;

Traditional:

• Placed near beginning of program file
• Uppercase only

Statements, Compound Statements

• Actions taken by the computer
• Numerous statement types (see pp. 90--91):
  • Processing
  • I/O
  • Declarations
  • Selection
  • Repetition
• Compound statement delimited by { }

The main function

• Required of every C++ program
• One form:

  int main()
  {
     // statements
     return 0;
  }
  

Some Basic C++ Statements

Arithmetic Expressions

Assignment operator: =

Assignment expression statement form:

variable = arithmeticExpression;

Arithmetic operators:

• + --- addition
• - --- subtraction
• * --- multiplication
• / --- division

Precedence, associativity

value = 1 + 2 * 3 + 4;
value = 10 - 8 - 4;

I/O Statements

• >> --- extraction operator
• cin
• << --- insertion operator
• cout

cout << "Enter two integers: ";
cin >> value1;
cin >> value2;
cout << "Their sum is: " << value1 + value2 << "." << endl;

Programming Style

The Goal: your program should be easy to read and understand

Points:

• Be generous with whitespace
• Clear, non-redundant comments
• One statement or declaration per line
• Manually split long statements onto several lines
• Indent compound blocks consistently (3 spaces)