1. User-defined Functions
Divide and Conquer

2. Definition of a Module One way in One way out
Executes the same – all of the time (predictable)
Highly “cohesive”

3. Function – Module by any other name
Principle module in C and C++ is a “function”
Three basic parts to function use (order not significant)
Definition – the programming
Prototype – alert to the compiler
Call – transfer of program control to the function

4. Function Definition
The block of code that tells the computer what to do
Has an identifying heading which contains a
Return type – the type of information created as a result of the execution
Function name – identifier so other parts of the program can reference (call) the block of code
Function parameters – transfers copies of data from other parts of the program

5. Basic Syntax A function can only return ONE value
double div_two( double val1, double val2) {
double result = 0.0;
if( val2 != 0.0)
result = val1/val2;
return result;
} // End of double div_two( double val1, double val2)
A function can only return ONE value

6. The Heading

7. The Body
Sends a copy of result back
to the calling block

8. The Prototype
Alerts the compiler that the specified programming block follows the main()
Is essentially a copy of the function heading followed by a semicolon
Example:
double div_two( double val1, double val2);
Placed prior to main()

9. The Call Transfers control of the program to the called function
Typically allows the copying of values from the calling code to the function (usually for processing)- these are generally called “arguments”
Assigns any returned value to an appropriate variable
Example:
double ans = div_two( 23.5, 12.4);
The values 23.5 and 12.4 are called “arguments of div_two”
They could (and most often are) variables. These would be considered a form of input for the function div_two().

10. Four general categories of Functions – based on parameters and return type
Does not receive data and does not return information
int transition( ) // Sometimes has a void return type {
cout << “Press <ENTER> to Continue”;
getline(cin, resp);
return 0;
} // End of int transition()

11. Receives parameters but does not return any values
void printData(string name, double balance) {
cout << name << “has a balance of” <<fixed << setprecision(2) << balance << endl; }

12. Has no parameters but returns a value
double inputPrice( ) {
double price = 0.0;
string price_str = “XXXX”;
cout << “Enter the wholesale price: “;
getline(cin, price_str);
while( (price_str.at(0) <=‘0’ )|| (price_str.at(0) >=‘9’))
cout << “Entry ERROR – Please enter a numeric value: “;
} //End of - while( (price_str.at(0) <=‘0’ )|| (price_str.at(0) >=‘9’))
price = atof(price_str.data());
return price;
}// End of - double inputPrice( )

13. Has parameters and a return value
double div_two( double val1, double val2) {
double result = 0.0;
if( val2 != 0.0)
result = val1/val2;
return result;
} // End of double div_two( double val1, double val2)

14. Now Look at Project 2