Lec 17B Project 2: Arrays
of Structs
1
Introduction
A common way to hold data is in an array.
A common way to represent data is with a
struct.
Many times you will need to put them both
together.
Accessing the array of structs is fairly easy,
once you get used to it.
2
Example--an inventory record
struct Record
{
string ID;
int Value;
string Description;
};
3
An Array of 5 Records
Record AutoParts[5];
AutoParts 0
1
2
3
4
ID
Value
Description
This is AutoParts[0]
It has 3 pieces: .ID, .Value and
.Description
4
Storage and Retrieval—By Fields
Record AutoParts[5];
AutoParts[0].ID=“3G45-A”;
AutoParts[0].Value=39.99;
AutoParts[0].Description=“Tire”;
AutoParts 0
ID
Value
Description
1
2
3
4
3G45-A
39.99
Tire
5
Storage and Retrieval—By Fields
Display AutoParts[0]
first cell in array
cout<<AutoParts[0].ID<<“ ”;
cout<<AutoParts[0].Value<<“ ”;
cout<<AutoParts[0].Description<<endl;
AutoParts 0
ID
Value
Description
1
2
3
4
3G45-A
39.99
Tire
cin works the same way!
cin>>AutoParts[0].ID >> (…etc)
6
Your Turn
Write C++ to store the information for a
Muffler, costing $89.89, and ID “1E73-M” at
index 4 of the AutoParts array
AutoParts 0
ID
Value
Description
1
2
3
4
3G45-A
39.99
Tire
7
Inputing Records using placeholders
string ID, Description;
float Value;
//read in a some values that need to be
stored
in >> ID >> Value >> Description;
//Store them in an array location
MyArray[0].ID = ID;
MyArray[0].Value = Value;
MyArray[0].Description = Description;
You can fill the entire array this way, like in a loop or
something (replacing [0] with [k] or loop counter)
Now you can do things like sort or print them
8
Storage and Retrieval—By whole Record
Record Blank;
Blank.ID=“------”;
Blank.Value=0.0;
Blank.Description=“------”;
AutoParts[1]=Blank;
AutoParts 0
ID
Value
Description
1
2
A “Blank” Record
Blank
-----0.0
------
3
4
3G45-A -----39.99
0.0
Tire
-----9
Storage and Retrieval—By whole Record
Record Purchase;
Purchase=AutoParts[0];
Display(Purchase);
A “Purchased” Part
Purchase
3G45-A
39.99
Tire
AutoParts 0
ID
Value
Description
1
2
3
4
3G45-A -----39.99
0.0
Tire
-----10
Storage and Retrieval—For Loops
//set the whole array to Blank
for ( int i =0; i < 5; i++ )
{ AutoParts[i].ID=“------”;
AutoParts[i].Value=0.0;
AutoParts[i].Description=“------”;
}
OR (simpler) This uses “aggregate” assignment
for ( int i =0; i < 10; i++ )
AutoParts[i] = Blank;
11
Function to Display a single Struct Record
void Display(Record rec)
{
cout<<rec.ID<<“ ”;
cout<<rec.Value<<“ ”;
cout<<rec.Description<<endl;
}
12
Display an Array of Struct Records
void DisplayAll( Record rec[ ], int N)
{
for ( int i =0; i < N; i++ )
{ cout<<“Record ”<<i<<“: ”;
cout<<rec[i].ID<<“ ”;
cout<<rec[i].Value<<“ ”;
cout<<rec[i].Description<<endl;
}
}
13
Your Turn
Make a function call to Display the last
AutoPart Record:
Make a function call to Display the whole
AutoPart array:
14
Before continuing….let’s see how to apply
this to project2
You have a file
You also have
struct Account
{
string name;
int ID, PIN;
};
How do you read the file into an array of Accounts?15
Prepare to read the file
1) Create an input file stream, open to accounts.txt
2) Create an array of Accounts, an integer k, and a
temp Account
16
Read the file
3) Read one line of the file into temp (or array cell k)
4) Extend with a while loop to read the whole file
17
Sorting—Selection Sort Variation
void Sort ( Record Array[], int size )
{
Record TempRecord;
int small_pos ;
for ( int i=0; i < size-1; i++ )
{
small_pos = i;
for ( int j = i+1; j < size; j++ )
18
Swap
{
if ( Array[small_pos].ID > Array[j].ID )
small_pos = j;
}
TempRecord = Array[i];
Array[i] = Array[small_pos];
Array[small_pos] = TempRecord;
}
}
Here the “key” field to
compare Records by is ID
19
Printing to a file
Formatting
for ( int i=0; i<size; i++ )
out << setw(15) << Array[i].ID <<setw(15)
<< Array[i].Value << setw(40)
<< Array[i].Description << endl;
20
Go to it!
You are now ready to complete problems 811 in Lab11Structs.cpp
21