1 Functions Knowledge Understanding of the structured design using function Skills Writing programs using user-defined functions and library functions

1

FunctionsFunctions

KnowledgeUnderstanding of the structured design using function

SkillsWriting programs using user-defined functions and library functions

TK1913-C ProgrammingTK1913-C Programming 22

An approach used to handle complexity in solving problems based on the “divide and conquer” strategy

A larger problem (more complex) is broken up into smaller problems (less complex)

The solution to the problem (a module) consists of a combination of solutions for the smaller problems (sub-modules)

Each sub-module also has its own input(s) and output(s)

Structural DecompositionStructural Decomposition


The results of structural decomposition may be illustrated using a diagram called a structure chart

It is intended to show the structural relationship between sub-modules that construct the problem solution and the data flow between them

Structure ChartsStructure Charts


Read 3 letters Output the first letterFind the first letter

Find the first letterbetween the 2 letters

Find the first letterbetween the 2 letters

letter1,letter2,letter3

firstLetter

firstLetter

firstLetter


firstLetter

letter1,letter2

firstLetter,

letter3

Input 3 letters andoutput the first letter

by chronological order


Top-down design is a method of building

programs based on solution structures derived

from structured decomposition

Solution to every sub-problem in the structure

chart is usually coded as a function in a program

Function is a subprogram which carries out a

specific task

Top-Down DesignTop-Down Design


Functions designed, written or defined by

programmers

Every user-defined function must have a

definition and a declaration (prototype).

A function must be called in order to execute the

statements contained in its definition

Function prototypes are usually placed before

their definitions in a program

User-Defined FunctionsUser-Defined Functions


Program to display 3 lines of characters

Display character line

Example:


Example:#include <stdio.h>void displayLine( );int main() {

int i;for (i=0; i < 3; i++)

displayLine( );}void displayLine( ) {

printf("#######\n");}

main( ) function

displayLine( ) function



int i;for (i=0; i < 3; i++)


printf("#######\n");}

displayLine( ) function prototype

displayLine( ) function



int i;for (i=0; i < 3; i++)


printf("#######\n");}

Function head



int i;for (i=0; i < 3; i++)


printf("#######\n");}

Function body



int i;for (i=0; i < 3; i++)

displayLine( ); }void displayLine( ) {

printf("#######\n");} Function call

- A call to displayLine( ) function



int i;for (i=0; i < 3; i++)


printf("#######\n");}

Another function call- a call to printf( ) library function



int i;for ( i=0 ; i < 3 ; i++ )


printf("#######\n");}

0i



int i;for ( i=0 ; i < 3 ; i++ )


printf("#######\n");}

0i



int i;for ( i=0 ; i < 3 ; i++ )


printf("#######\n");}

0i


#include <stdio.h>void displayLine( );int main() {

int i;for ( i=0 ; i < 3 ; i++ )


printf("#######\n");}

Example:

#######_



int i;for ( i=0 ; i < 3 ; i++ )


printf("#######\n");}

0i

#######_



int i;for ( i=0 ; i < 3 ; i++ )


printf("#######\n");}

1i

#######_



int i;for ( i=0 ; i < 3 ; i++ )


printf("#######\n");}

1i

#######_



int i;for ( i=0 ; i < 3 ; i++ )


printf("#######\n");}

1i

#######_



int i;for ( i=0 ; i < 3 ; i++ )


printf("#######\n");}

Example:

############## _



int i;for ( i=0 ; i < 3 ; i++ )


printf("#######\n");}

1i

############## _



int i;for ( i=0 ; i < 3 ; i++ )


printf("#######\n");}

2i

############## _



int i;for ( i=0 ; i < 3 ; i++ )


printf("#######\n");}

2i

############## _



int i;for ( i=0 ; i < 3 ; i++ )


printf("#######\n");}

2i

##############_



int i;for ( i=0 ; i < 3 ; i++ )


printf("#######\n");}

Example:

##################### _



int i;for ( i=0 ; i < 3 ; i++ )


printf("#######\n");}

2i

##################### _



int i;for ( i=0 ; i < 3 ; i++ )


printf("#######\n");}

3i

##################### _



int i;for ( i=0 ; i < 3 ; i++ )


printf("#######\n");}

3i

##################### _



int i;for ( i=0 ; i < 3 ; i++ )


printf("#######\n");}

3i

##################### _


To execute a function, it must first be called with the following information: Stating the function name Providing a certain information (parameter)

Syntax for a function call:function_name( actual_parameter_list );

function_name – the function name that is to be called actual_parameter_list – is a list of information which is

required to execute a function The number of parameters provided must be the same as

defined in the function definition

Function CallsFunction Calls


A function prototype declares a certain information

pertaining to the function

C compiler uses the information in the function

prototype for compiling function calls in a program

Syntax for function prototyping:

data_type function_name( parameter_definition_list); This form is similar to the function definition head

Function PrototypesFunction Prototypes


Function characteristics:

With parameters? Returns a value?

Function CharacteristicsFunction Characteristics


A function which has no parameter and return value may be defined as follows:

void function_name() { local_variable _declaration;

executable_function_statements;}

Function which does not return any value

void

Function without any parameter

( )

Function Without Parameter Function Without Parameter and Not Returning Any Valueand Not Returning Any Value


Example:#include <stdio.h>void inputComputeAndOutputArea( );int main() {

inputComputeAndOutputArea( );}void inputComputeAndOutputArea( ) {

int width, height, area;scanf("%d%d", &width, &height);area = width * height;printf(“Area: %d\n", area);

}


Example:#include <stdio.h>void inputComputeAndOutputArea( );int main() {



}


#include <stdio.h>void inputComputeAndOutputArea( );int main() {



}

Example:

_

width

height

area

???

???

???





}

Example:

12 8_

width

height

area

12

8

???





}

Example:

12 8_

width

height

area

12

8

96


#include <stdio.h>void input_compute_and_output_area( );int main() {



}

Example:

12 8Area: 96_

width

height

area

12

8

96





}

Example:

12 8Area: 96_


In structural decomposition, the solution to a sub-problem may require some specific data

Input 3 letters and output the first letter by chronological order

Read 3 letters Output first letterFind first letter

letter 1,letter 2,letter 3 first

letter

letter 1,letter 2,letter 3

firstletter

Function With ParametersFunction With Parameters


For a C function, a parameter needs to be defined for each data to be handed by a caller

void outputFirstLetter(char firstLetter ) {printf(“First letter: %c\n", firstLetter);

}The caller to this function needs to hand a data of type char. In this function, the data is kept in a variable named firstLetter



Parameter’s name is optional in function prototype

void displayArea(int width, int height) {printf(“Area: %d\n", width*height);

}

The following function prototypes are valid:

void displayArea(int width, int height);void displayArea(int, int);


Example:#include <stdio.h>void computeAndOutputArea(int width, int height);int main() {

int rectWidth, rectHeight;scanf(“%d%d”, &rectWidth, &rectHeight);computeAndOutputArea(rectWidth, rectHeight);

}void computeAndOutputArea(int width, int height) {

printf(“Area: %d\n", width * height);}

Example:#include <stdio.h>void computeAndOutputArea(int width, int height);int main() {




???

???

rectWidth

rectHeight

_

Contoh:

#include <stdio.h>void computeAndOutputArea(int width, int height);int main() {




7

8

rectWidth

rectHeight

7 8_

Example:





7

8

rectWidth

rectHeight

7 8_

Example:





7

8

rectWidth

rectHeight

7 8_

7

8

width

height



}void computeAndOutputArea( int width, int height) {


Example:

7 8Area: 56_

7

8

width

height



}void computeAndOutputArea( int width, int height) {


Example:

7 8Area: 56_

7

8

rectWidth

rectHeight


In structural decomposition, the solution to a sub-problem may return a data/info

Input 3 letters and Output first letter

Read 3 letters Output first letterFind first letter


firstLetter


firstLetter

Function That Returns a ValueFunction That Returns a Value


Besides receiving data from the caller, a function can also return a value to the caller.

Example:

int computeRectArea(int width, int height) {int area;area = width * height;return area;

}



The data type of the value being returned must

be specified in the function definition.return_type function_name(parameter_list) {

local_variable_definition;statements;

}

Value type being returned by the function

return_type



A function returns a value via a return statement

When a return statement is executed, program control is returned to the caller along with the return value

Example:int computeRectArea(int width, int height) {

int area;area = width * height;return area;

}

return Statementreturn Statement

Example:#include <stdio.h>int computeArea(int width, int height);void outputArea(int area);int main() {

int rectWidth, rectHeight, rectArea;scanf("%d%d", &rectWidth, &rectHeight);rectArea = computeArea(rectWidth, rectHeight);outputArea(rectArea);

}int computeArea(int width, int height) {

return width * height;}void outputArea(int area) {

printf(“Rectangle area: %d\n", area);}






???

???

rectWidth

rectHeight

???

rectArea

_






7

11

rectWidth

rectHeight

???

rectArea

7 11_






7

11

rectWidth

rectHeight

???

rectArea

7 11_






7

11

rectWidth

rectHeight

???

rectArea

7 11_

7 11

width height

#include <stdio.h>int computeArea(int width, int height);void outputArea(int area);int main() {





Example:

7 11_

7 11width height

77






Example:

7 11_

7

11

rectWidth

rectHeight

77

rectArea






Example:

7 11_

7

11

rectWidth

rectHeight

77

rectArea






Example:

7 11_

7

11rectWidth

rectHeight

77

rectArea

77

area






Example:

7 11_

77

area

7 11Rectangle area: 77_






Example:


7

11

rectWidth

rectHeight

77

rectArea






Example:


7

11

rectWidth

rectHeight

77rectArea


In a function which does not return any value, the return statement (without expression) will result in the program control being returned to the caller.



Example:void displayLine(int length) {

int i = 0;while (1) {

if (i == length) {printf(“\n”);return;

}printf(“*”);i++;

}}



Variables which are defined in a function can only be used within that function. This type of variables is known as local variable.

Example,

void displayLine(int lineNum) {int i;for (i = 0; i < lineNum; i++)

printf("#########\n");}

Local variables

Local VariablesLocal Variables


Local variable cannot be accessed outside the function which defines it


int computeRectArea(int, int);int main() {

int rectWidth, rectHeight, rectArea;

scanf("%d%d", &rectWidth, &rectHeight);rectArea = computeRectArea(rectWidth, rectHeight);printf(“Rectangle area: %d", area);

}int computeRectArea(int width, int height) {


}



int rectWidth, rectHeight, rectArea;

scanf("%d%d", &rectWidth, &rectHeight);rectArea = computeRectArea(rectWidth, rectHeight);printf(“Rectangle area: %d", area);



}

The local variable area is only for usage within function computeRectArea()-The function which defines it



int rectWidth, rectHeight;int rectArea;scanf("%d%d", &rectWidth, &rectHeight);rectArea = computeRectArea(rectWidth, rectHeight);printf(“Rectangle area: %d", area);



}

Variable area in function computeRectArea() cannot be accessed here.

ERROR!


Documents

1 Functions Knowledge Understanding of the structured design using function Skills Writing programs using user-defined functions and library functions