FunctionsFunctions Data Flow Scope

local global

part 4part 4

Data FlowData Flow

Data flow is the direction of the information flow between the function and its caller.

Adding data flow documentation to the function interface is helpful.

The flow could be into a function, out of a function or both.

Parameter and Data FlowParameter and Data Flow

pass data into a function /* in *//* in */

pass data out of a function /* out *//* out */

pass data into and out of a function /* inout *//* inout */

Examples

void myFunction( /* in */ double nana, /* in */ int count)

void yourFunction( /* out */ int& num1, /* out */ int& num2)

void ourFunction( /* in */ int alpha, /* inout */ int& beta)

Parameter and Data FlowParameter and Data Flow

Parameter and Data FlowParameter and Data Flow

To be certain a function does what you want it to do, write value of variables as you enter and exit a function.

Put the output statement into a function and call it whenever you need it.

void ShowIt(void){ cout<< var1<< ‘\t’ <<var2<< ‘\t’ <<var3<< ‘\n’;}

*

Data Flow - ExampleData Flow - Example#include<iostream>using namespace std;void getTemp(double&);void activity(double);void convertCtoF(double&);

void main(void){

double temperature;getTemp(temperature);activity(temperature);

}

Data Flow - ExampleData Flow - Examplevoid getTemp(/* */ double& temp){{

cout<<"Enter the temperature in degrees C: ";cin>> temp;cout<<"The current temperature is "

<<temp<<" degrees celsius."<<endl;convertCtoF(temp);

}}

void convertCtoF( /* */ double& temp){{

temp=(1.8)*temp +32;cout<<"This equals "<<temp

<<" degrees Fahrenheit."<<endl;}}

out

inout

* *

Data Flow - ExampleData Flow - Examplevoid activity(/* */ double temp){{

cout<<"The recommended activity is ";if(temp>85)

cout<<"swimming."<<endl;else if(temp>70)

cout<<"tennis."<<endl;else if(temp>35)

cout<<"golf."<<endl;else if(temp>10)

cout<<"skiing."<<endl;else

cout<<"dancing."<<endl;}}

in

*

ScopeScope

A function is like a black box:You know what goes in and what comes out, but you do not know what happens inside the box.

ScopeScopeThe section of the program where the variable is valid

(known or visible).

local = available to only one functionor block. Used to limit access.

global = available multiple functions or blocks. Used to save call time or reduce complexity of call sequence

ScopeScope

Local:The scope of an identifier declared inside a blockblock extends from the point of declaration to the end of that block.

Global:The scope of an identifier declared outside all functions and classes extends from the point of declaration to the end of the source file.

* *

Block = { }

Local VariablesLocal Variables declared within a function definition

private to a function definition

variables in different functions are totally independent

different functions can have variables with the same names; however, each variable will have its own memory address

actually applies to any block

* * * *

int x = 3;int x = 3; // global because before main

void main(void){ // no variables local to main( )

void myfunction( ); // prototype

cout <<"x = "<<x<<" before the function call.\n"; myfunction( ); cout <<"x = "<<x<<" after the function call.\n";

}

void myfunction( ){

int r; // local to myfunction( ) r = ++x; cout <<"r = "<<r<<" within the function.\n";

}

// what happens to global x?

ScopeScope

OUTPUTx = 3 before the function call.r = 4 within the function. x = 4 after the function call.

Example Example - ReadValuesvoid main(void){ int a, b, c; float avg;

void ReadValues( int&, int&, int& ); void Adjust( int&, int&, int& ); float Average( int, int, int ); void WriteResults( int, int, int, int, float );

ReadValues(a, b, c); Adjust(a, b, c); avg = Average(a, b, c); WriteResults(a, b, c, a + b + c, avg);

}

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Example Example - ReadValues

1. main declares and calls ReadValues

2. ReadValues declares and calls ReadOne [3x]

3. main declares and calls Adjust

4. main declares and calls Average

5. main declares and calls WriteResults

* * * *

Example Example - ReadValuesvoid ReadValues( /* */ int& x, /* */ int& y,

/* */ int& z ){ void ReadOne( char, int& );

ReadOne('1', x ); ReadOne('2', y ); ReadOne('3', z );

return;}

* *

outout

out

Example Example - ReadOne

void ReadOne( /* */ char number,

/* */ int& item )

{

cout << "Enter value " << number << ": ";

cin >> item;

return;

}

* *

in

out

Example Example - Adjust

void Adjust( /* */ int& i, /* */ int& j, /* */ int& k ){ int smallest; smallest = i;

if (j < smallest) i = i - smallest; smallest = j; j = j - smallest; if (k < smallest) k = k - smallest; smallest = k; return;

}

* *

inoutinout

inout

Example Example - Average

float Average( /* */ int item1, /* */ int item2,

/* */ int item3 )

{

int total;

total = item1 + item2 + item3;

return float(total) / 3;

}

* *

in in

in

Example Example - WriteResults

void WriteResults( /* */ int item1, /* */ int item2, /* */ int item3, /* */ int total, /* */ float average ){ cout << "Adjusted values: " << item1 << ", " << item2 << ", " << item3 << '\n'

<< "Sum: " << total << " Average: " << average << '\n';

return;}

* *

in

ininin

in

ReadValues Adjust Average WriteResults

ReadOne

Main

Enter value 1: 23Enter value 2: 56Enter value 3: 78Adjusted values: 0, 33, 55Sum: 88 Average: 29.3333

Common ErrorsCommon Errors Wrong positioning of the called function Wrong positioning of the called function

prototypeprototype

Terminating a function header with a Terminating a function header with a ;; Forgetting the data type of a function’s Forgetting the data type of a function’s

parameterparameter Remember the NOT rule:Remember the NOT rule:

NNumberumber OOrderrder TTypeype