1 Lecture 16:User-Definded function I Introduction to Computer Science Spring 2006.

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Lecture 16:User-Definded function I

Introduction to Computer Science

Spring 2006

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Predefined Functions To use these functions you need to:

Include the correct header file Know the name of the function Know the number of parameters, if any Know the data type of each parameter Know the data type of the value

computed by the function, called the type of the function

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Predefined Functions : Value-Returning Functions Because the value returned by a value-

returning function is unique, we must:

Save the value for further calculation

Use the value in some calculation

Print the value

A value-returning function is used in an assignment or in an output statement

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Use of standard function pow#include <iostream>

using namespace std;int main(){

double u,v;double result;u = 4.2;v = 3.0;

return 0;}

#include <cmath>

result=pow(u, v);

cout << u << " to the power of " << v << " = " << pow(u, v) << endl;

cout << "u = " << u << endl;

u = u + pow(3, 3);

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User-Defined Functions Void functions: do not have a data

type Value-returning functions: have a

data type

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#include <iostream>using namespace std;

int main(){ int i, j; int k;

cin>>i>>j;

if (i > j) { k = i; } else { k = j; } cout << "The max is " << k << endl;

return 0;}


/* Function Declarations */int FindMax(int n1, int n2);void PrintMax(int someNumber);

int main(){ int i, j; int k; cin>>i>>j;

k = FindMax(i,j); PrintMax(k); // Prints Max Value

return 0;}

/* Function Definitions */int FindMax(int n1, int n2){ if (n1 > n2) { return n1; } else { return n2; }}

/* Function Definitions */void PrintMax(int someNumber){ cout << "The max is " << someNumber << endl;}

Value-returning functions

Void functions

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Value-Returning Functions Because the value returned by a value-

returning function is unique, we must:

Save the value for further calculation

Use the value in some calculation

Print the value

A value-returning function is used in an assignment or in an output statement

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/* Function Declarations */int FindMax(int n1, int n2);


k = FindMax(i,j);

return 0;}

/* Function Definitions */int FindMax(int n1, int n2){ if (n1 > n2) { return n1; } else { return n2; }}

cout << "The max is "<< FindMax(i,j) << endl;k =FindMax(i, j) + 1;

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Value-Returning Functions: function definition

Properties that form the function definition: Heading:

1. Name of the function

2. Number of parameters

3. Data type of each parameter

4. Function Type (type of the value returned by the function)

Body:

1. Code required to accomplish the task (the body of the function)

The syntax of the function definition is:

functionType functionName(formal parameter list){

statements}

The syntax of the formal parameter list is:

dataType identifier, dataType identifier, ...

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Value-Returning Functions: function definition

int FindMax(int n1, int n2){ if (n1 > n2) { return n1; } else { return n2; }}

Function Heading

int FindMax(int n1, int n2)

Function Body

Function Type

Function Name

Formal parameter list

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Value-Returning Functions: call a value-returning function To call a value-returning function:

Use its name, with the actual parameters (if any) in parentheses

The syntax for a function call is:

functionName(actual parameter list)

The syntax for the actual parameter list is:

expression or variable,expression or variable, ...

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k = FindMax( i, j ) ;

return 0;}

/* Function Definitions */int FindMax( int n1, int n2 ){ if (n1 > n2) { return n1; } else { return n2; }}

Actual parameter list

Function Name

Call a Value-returning Function

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Function Prototype Function Prototype: function heading without the body

of the function The syntax is:

functionType functionName(parameter list); It is not necessary to specify the variable name in the

parameter list The data type of each parameter must be specified

Function prototypes appear before any function definition

The compiler translates these first

The compiler can then correctly translate a function call

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return 0;}


Function Prototype

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Value-Returning Functions (continued)

Formal Parameter: variable declared in the heading

Actual Parameter: variable or expression listed in a call to a function

There is a one-to-one correspondence between actual and formal parameters

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return 0;}


Actual parameter list

Formal parameter list

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Functions The formal parameter list can be empty If the formal parameter list is empty

Parentheses are still needed Function heading of the value-returning

function takes either of the following forms: functionType functionName() functionType functionName(void)

In a function call the actual parameter is empty

A call to a value-returning function with an empty formal parameter list is: functionName()

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Value-Returning Functions :The return Statement

Once the function computes the value, the function returns the value via the return statement

The syntax of the return statement is:return expression or variable;

When a return statement executes Function immediately terminates Control goes back to the caller

When a return statement executes in the function main, the program terminates

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Flow of Execution Execution always begins at

The first statement in the function main no matter where main is placed in the program

Other functions are executed only when they are called

A function call statement results in

Transfer of control to the first statement in the body of the called function

After the last statement of the called function is executed

Control is passed back to the point immediately following the function call

A value-returning function returns a value

After executing the function

The value that the function returns replaces the function call statement

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return 0;}


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End of lecture 16

Thank you!

1 Lecture 16:User-Definded function I Introduction to Computer Science Spring 2006.

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