Structures
 

    A structure is a group of several components or members. Unlike the components of an array the components of a structure may be of different types. Once declared structs behave like scalar data types.

  1. Declarations. You declare a structure by listing its members along with their data types between curly braces.
    2. struct course
 { 
   int   students;
   float average;
 };

 course mw;
 course rgc[10];
 course *ms;
  2. Accessing fields. Fields are accessed using the dot (.) operator.
    3. mw.students= 23;
mw.students = rgc[2].students + 1;
(*ms).students=12;
  3. Complex Structures Members need not be scalar. They may be arrays, other structures.
    4. struct course
{
 int   students;
 float average;
 int   grades[35];
};

course c;

c.grades[3]=4;

struct schedule
{
   int room;
   int time;
   int day;
};

struct course
{
  int      students;
  float    average;
  int      grades[35];
  schedule when;
};

course c;

 c.when.room =127;
  4. Pointers to structures
    5. course *c;

(*c).average =34.5; note not *c.average

 c->average = 3.14;
  5. Initializing Structures.
    6. course mw = {32,0.0};

  6. sizeof operator on structures.

    7. sizeof(course);

  7. Arrays of structures.

    8. course rgc[30];

  8. Self referencing structures.
    9. struct line
{ 
    char data[80];
    line *next;
};

line start;

  9. Example.

    Adding a list of fractions 

    Enter a list of fractions to add
 Enter e to end
1 1/2

Adding 1 1/2 +  = 1 1/2
3 7/8

Adding 3 7/8 + 1 1/2 = 5 3/8
4

Adding 4  + 5 3/8 = 9 3/8
3/5

Adding 3/5 + 9 3/8 = 9 39/40
e
Press any key to continue
    Header Module Sfraction.h 
    //
// Fractions Program in Strucures.
//
#ifndef SFRACT
#define SFRACT


struct Fraction {
   int whole;
   int numerator;
   int denominator;
};

void     displayFraction(Fraction);
int      getFraction(Fraction&);
Fraction addFraction(Fraction, Fraction);
int      gcd(int,int);

#endif
    Main Module Sfraction.cpp 
    //
//  main
//

#include <iostream>
#include "Sfraction.h"

using namespace std;

int main()
{
   Fraction sum, item;

   sum.whole=sum.numerator=0;
   sum.denominator=1;

   cout << "Enter a list of fractions to add" << endl
        << " Enter e to end" << endl;

   while(getFraction(item)){
      cout << endl << "Adding ";
      displayFraction(item);
      cout << " + ";
      displayFraction(sum);
      sum=addFraction(sum,item);
      cout << " = ";
      displayFraction(sum);
      cout << endl;
   }

   system("pause");
   return 0;
}
    Code Module SfractionM.cpp 
    //
// Modules
//
#include "Sfraction.h"
#include <iostream>
#include <string.h>
#include <stdlib.h>

using namesapce std;
//
// Get a Fraction
//
int getFraction(Fraction& k)
{
   char *p,line[81];
   int a[3]={0,0,0};
   int count=0;
   cin.getline(line,80);
   if(line[0] == 'e') return 0;
   if(cin.eof())      return 0;
   p=strtok(line," /");
   do {
      a[count]=atoi(p);
      count++;
      p=strtok(NULL," /");
   } while(p);
   count--;
   k.whole=k.numerator=0;
   k.denominator=1;
   switch (count) {
      case 0: k.whole=a[0]; break;
      case 1: k.numerator=a[0],k.denominator=a[1]; break;
      case 2: k.whole=a[0],k.numerator=a[1],k.denominator=a[2];
   }
   return 1;
}

// 
// Display a Fraction
//
void displayFraction(Fraction x)
{
   if(x.whole)     cout << x.whole << " ";
   if(x.numerator) cout << x.numerator << "/" 
                        << x.denominator;
}

//
//   add two fractions
//
Fraction addFraction(Fraction a, Fraction b)
{
   Fraction answer;
   int  common,worka,workb,numer,x;

   // Compute the common denominator
   common=a.denominator * b.denominator;

   // convert from mixed fractions.
   worka = a.whole * a.denominator + a.numerator;
   workb = b.whole * b.denominator + b.numerator;

   // compute the numerator
   numer = worka * b.denominator + workb * a.denominator;

   // save whole answer
   answer.whole= numer / common;

   // reduce to lowest term
   numer %= common;
   x=gcd(common,numer);
   answer.numerator=numer/x;
   answer.denominator=common/x;

   return answer;
}

//
// Euler's Algorithm to find the greatest common divisor
//
int gcd(int a, int b)
{
   if(b) return(gcd(b,a%b));
   else return a;
}