1 Lec 17B Project 2: Arrays of Structs. 2 Introduction A common way to hold data is in an array. A...
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Transcript of 1 Lec 17B Project 2: Arrays of Structs. 2 Introduction A common way to hold data is in an array. A...
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Lec 17B Project 2: Arrays of Structs
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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.
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Example--an inventory record
struct Record
{
string ID;
int Value;
string Description;
};
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An Array of 5 Records
Record AutoParts[5];
AutoParts 0 1 2 3 4
This is AutoParts[0]
It has 3 pieces: .ID, .Value and
.Description
ID
Value
Description
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Storage and Retrieval—By Fields
Record AutoParts[5];
AutoParts[0].ID=“3G45-A”;
AutoParts[0].Value=39.99;
AutoParts[0].Description=“Tire”;
AutoParts 0 1 2 3 4
3G45-A
39.99
Tire
ID
Value
Description
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Storage and Retrieval—By FieldsDisplay AutoParts[0] first cell in array
cout<<AutoParts[0].ID<<“ ”;cout<<AutoParts[0].Value<<“ ”;cout<<AutoParts[0].Description<<endl;
AutoParts 0 1 2 3 4
cin works the same way! cin>>AutoParts[0].ID >> (…etc)
3G45-A
39.99
Tire
ID
Value
Description
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Your TurnWrite C++ to store the information for a Muffler, costing $89.89, and ID “1E73-M” at index 4 of the AutoParts array
AutoParts 0 1 2 3 4
3G45-A
39.99
Tire
ID
Value
Description
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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
Inputing Records using placeholders
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Storage and Retrieval—By whole RecordRecord Blank;
Blank.ID=“------”;
Blank.Value=0.0;
Blank.Description=“------”;
AutoParts[1]=Blank;
AutoParts 0 1 2 3 43G45-A ------
39.99 0.0
Tire ------
ID
Value
Description
A “Blank” Record
------
0.0
------
Blank
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Storage and Retrieval—By whole RecordRecord Purchase;
Purchase=AutoParts[0];
Display(Purchase);
AutoParts 0 1 2 3 43G45-A ------
39.99 0.0
Tire ------
ID
Value
Description
A “Purchased” Part
3G45-A
39.99
Tire
Purchase
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//set the whole array to Blankfor ( 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;
Storage and Retrieval—For Loops
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void Display(Record rec)
{
cout<<rec.ID<<“ ”;
cout<<rec.Value<<“ ”; cout<<rec.Description<<endl;
}
Function to Display a single Struct Record
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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;
}
}
Display an Array of Struct Records
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Your Turn
Make a function call to Display the last AutoPart Record:
Make a function call to Display the whole AutoPart array:
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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;
float balance;};
How do you read the file into an array of Accounts?
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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
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Read the file3) Read one line of the file into temp (or array cell k)
4) Extend with a while loop to read the whole file
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Sorting—Selection Sort Variationvoid 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++ )
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{
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
Swap
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Printing to a file
for ( int i=0; i<size; i++ )
out << setw(15) << Array[i].ID <<setw(15)
<< Array[i].Value << setw(40)
<< Array[i].Description << endl;
Formatting
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Go to it!
You are now ready to complete problems 8-11 in Lab17Structs.cpp
