Functions
CIS 230
01-Feb-06
Summary Slide
• Using Functions
• Mathematical
Functions
• Misc. Functions
• Naming Conventions
• Writing Functions
– Function Prototype
– Function Call
– Function Definition
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Variable Declaration
Variable Scope
Pass by Value
Function Overloading
Default Parameter
Values
Summary Slide (cont.)
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Variable Declaration
Variable Scope
Pass by Value
Function Overloading
Default Parameter Values
Using Functions
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Name of the function
What it does
Type of data required
Type of data returned
Library required
Using Functions
• Function called by giving function’s name
and passing data to it
• Called function: Function summoned into
action
• Calling function: Origination of function
call
Mathematical Functions
• #include <cmath>
Mathematical Functions
Mathematical Functions
Math:
| -8.39 | = 8.39
210 = 1024
e-3.2 = 0.0407622
C++:
abs(-8.39) = 8.39
pow(2,10) = 1024
exp(-3.2) = 0.0407622
Mathematical Functions
• Storing returned Data:
int pos_val;
pos_val = abs(-4);
cout << pos_val;
Misc. Functions
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#include <cctype>
tolower(value)
toupper(value)
isalpha(value)
isdigit(value)
Instead of:
if (again == ‘y’ || again == ‘Y’)
Use:
if (( again = tolower(again) == ‘y’)
cin >> invalue;
if (isalpha(invalue))
Or:
do
{
cin >> invalue;
} while (!isalpha(invalue))
Functions: Naming Conventions
Writing Functions
• Function Declaration/Prototype
– Return type
– Data type and order of values
• Function call
– Name of function
– Arguments
• Function Definition
– Function Header
– Function Body
Writing Functions
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Functions may receive none or several
values (parameters)
Values are passed (arguments) to
special variables (parameters) within the
function
Parameters are identified inside the ( )
Functions generally return one value
Function Prototype
returnDataType functionName (argument data types);
int calcTotal ( int, int );
double swap ( int, char, char, double );
.h Files
// Header file for function: x
// Name:
// last modified:
#ifndef X_H
#define X_H
// header file contents:
// any named constant
declarations?
//
// header of function ended
with semicolon
#endif
// Header file for function:
calcTotal
// Name: B. Gilden
// Last modified: 30-Jan-06
#ifndef calcTotal_H
#define calcTotal_H
int calcTotal ( int, int );
#endif
Function Call
#include “functionName.h”
int main ( ) {
int first, second, answer;
cout << “Enter two values to sum from the \n”
cout << “first to the second : “;
cin >> first >> second;
if ( first <= second ) {
answer = calcTotal (first, second);
cout << “The total is “ << answer << ‘\n’;
else
cout << “The values were not valid \n”;
}
Function Definition
Formal Parameter List
type functionName ( type var1, type var2, … )
{
// Named constants;
// Variable declarations;
// Other C++ statements;
return variable;
}
Function
Header
Function
Body
functionName.cpp
// Header commments
int calcTotal ( int a, int b )
{
int counter, sum;
sum = 0;
for ( counter = 1; counter <= b; ++counter )
sum = sum + counter;
return sum;
}
Compiling
Assumptions:
• main () -> main.cpp
• main ()
– includes “calcTotal.h”
– makes a call to
calcTotal()
• calcTotal.h
• calcTotal.cpp
>g++ -c main.cpp
>g++ -c calcTotal.cpp
Produces:
main.o calcTotal.o
>g++ -o program main.o calcTotal.o
Produces:
program
(the executable)
OR…
>g++ -o program main.cpp calcTotal.cpp
Variable Declaration
1. Outside a function
(global)
2. In the parameter
area
3. Inside the function
// 1. outside - global
int total;
// 2. parameter area
void sum (int a, int b)
{
// 3. inside the function
int c;
}
Variable Scope
• Global variables
• Local variables
Pass by Value
• Function receives copies of the values
• Function cannot access/change the calling
function’s variables.
• Function may return at most one value.
Function Overloading
• Permits the same function to be defined
for different argument data types.
• Second function, same name
• Parameters must be different
Function Overloading
• Write a function to find
the larger of two values.
int max (int a, int b)
{
if (a >= b)
return a;
else
return b;
}
• What about floating point
values?
float max (float x, float y)
{
if (x >= y)
return x;
else
return y;
}
Function Overloading
• Write a function that calculates the
area of a rectangle.
• A square is a rectangle,
with sides the same length.
float rectArea (float length, float width)
{
float area;
area = length * width;
return area;
}
float rectArea (float length)
{
float area;
area = length * length;
return area;
}
Invoked:
result = rectArea(x,y);
Invoked:
result = rectArea(x);
Default Parameter Values
• Assign the value in the prototype
• non-default(s) first, defaults last:
– int sample (int, char=‘a’, int = 7);
– int example (int, int, double = 6.78);
• Calling the function:
– answer = sample (t, ch, w); // no defaults
– answer = sample (t, ch); // last default (7) used
– answer== sample (t); //defaults ‘a’ and 7 used
• NOT:
– answer = sample (t, ,w); //This will NOT work!