Accessing Structure Members

individual structure members are accessed through the use of a period, generally called the dot operator. For example, the following code will assign the value 60.0 to the first_exam field of the structure variable varA declared earlier

varA.first_exam=60.0;

The structure variable name, followed by a period and the member name, refers to that member. All structure elements are accessed in the same way, the general form is

structure_varname.member_name

If you wish to access the individual elements of the array grade.name, you can index name. For example you can print the contents of grade.name one character at a time by using this code

int t;
for(t=0;grade.name[t];t++)
cout <<grade.name[t];

Structure may be arrayed. To declare an array of structures, you must first define a structure, then declare an array of its type. For example to declare 100-element array of structures of type grade you would write

grade eml3002[28];// defines structure for 28 students in eml3002

To access a specific structure, you must index the structure name. For example to print second exam of second student you would write

cout<<eml3002[1].second_exam;

Like all array variables, arrays of structures begin their indexing at zero.

Example
/* A simple grade record program */ #include<iostream.h>
#include<ctype.h>
#include<string.h>
#include<stdlib.h>

const int size=2; /*defines the number of student in a class, const modifier fixes the value of size through out the program */

struct grades{
char name[20]; // Name of a student with 20 characters
int ssn; //Social security numbers
double first_exam;// first exam
double second_exam;//second exam
float homework;//homework
double final;// final
} eml3002[size];

/* The program will provide these three options
1. Enter information
2. Display information
3. Modify information */
void enter(), init_list(), display(); // prototypes of functions
void update(), input(int i);// prototypes of functions

int menu();//prototype of functions

main()
{
char choice; //defines a character
init_list(); //initialize the structure array

for(;;){

choice=menu();// menu() displays the options and returns the user selection
switch(choice){
case 'e':enter();
break;
case 'd':display();
break;
case 'u':update();
break;
case 'q':return 0;
}
}
}

// Initializing the eml3002 array

{
int t;
// for space use the null character '$\backslash$0'
for(t=0;t<size;t++) *eml3002[t].name= '$\backslash$0';
}

// Get a menu selection
menu()
{
char ch;
cout <<'$\backslash$n';
do{
cout <<"(E)nter$\backslash$n";
cout <<"(D)isplay$\backslash$n";
cout <<"(U)pdate$\backslash$n";
cout <<"(Q)uit$\backslash$n$\backslash$n";
cout <<"Choose one:";
cin >>ch;
} while(!strchr("eduq",tolower(ch)));
return tolower(ch);
}

/* The program uses another C++ library functions strchr( char *str, char ch). This function searches the string pointed by str for an occurance of the character in ch. If no match is found a null is returned*/
// Enter items into the list

void enter()
{
int i;
// find the first free structure

for (i=0;i<size;i++)
if(!*eml3002[i].name)break;
// i will equal size if the list is full
if(i==size){
cout <<"List full$\backslash$n";
return;
} input(i);
}

//Input the information
void input(int i)
{
char str[80];
// enter the information
cout <<"Name: ";
cin >>eml3002[i].name;// last name
cout << "SSN :";// last 4 digits
cin >> eml3002[i].ssn;
cout << "First Exam: ";
cin >> eml3002[i].first_exam;// double
cout <<" Second Exam: "; cin >>eml3002[i].second_exam;
cout <<"Homework: ";
cin >> eml3002[i].homework;
cout << "Final: "; cin >> eml3002[i].final;
}

// modify an exiting grade

void update()
{
int i;
char mname[80];
cout << "Enter name:";
cin >>mname;
for(i=0;i<size;i++)
if(!strcmp(mname,eml3002[i].name)) break;// uses a library function
if(i==size){
cout << "name not found$\backslash$n";
return;
}
cout << "Enter new information. $\backslash$n";
input(i);

}

// Display the list
void display()
{
int t;
for(t=0;t<size;t++){
if(*eml3002[t].name){
cout << eml3002[t].name <<'$\backslash$n';
cout << "SSN :" <<eml3002[t].ssn <<'$\backslash$n';
cout << "First Exam " <<eml3002[t].first_exam <<'$\backslash$n';
cout << "Second Exam " <<eml3002[t].second_exam<<'$\backslash$n';
cout <<"Homework " << eml3002[t].homework<<'$\backslash$n';
cout <<"Final "<< eml3002[t].final<<'$\backslash$n';
}
}
}

Activity For this activity the

• first exam 20%
• second exam 20%
• hw, 20%
• final %40

1.

use the above program to enter the expected grades for your team members in this class

2.

modify the program to include an additional grade for final project which worth 20%. This will modify the final grade to be also 20%.