EKT120_WEEK05_FUNCTIONS1

8/12/2019 EKT120_WEEK05_FUNCTIONS1

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UniMAP SemII-09/10 EKT120: Computer Programming 1

Week 5Functions (1)


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Outline Why use functions? Functions in C

Pre-defined functions User-defined functions

Function prototypes Function definitions Function calls What about number, order and type of parameter? Functions that do not return a value Functions that return a value Miscellaneous about functions Sample application Scope and mechanics of passing values to functions


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Why use functions? Let say you want to print one row of number 8 and one row of number 9

#include int main()

{ int i, j;

//print one row of number 8for(i=1; i


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Why use functions? It seems that you are doing the same

thing twice!!(i.e. printing two rows of

numbers)

This is wasting time and not flexible!!

So, need to use function


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Why use functions?#include void display(int); //function prototypeint main(){

display(8); //function calldisplay(9); //function callreturn 0;

}

void display(int value) //function definition{ int i;for(i=1; i


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Functions in C Functions can be created to execute small,

frequently-used tasks In C, there are predefined functionsor sometimes

called standard functions, and there are user-defined functions.

Predefined functionsare already availablefunctions that can be used, called library

The usage is like stdio.h, in which the libraryname must be #includedat the top of the sourcecode (preprocessor directive)


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Predefined Functions (Library) Common libraries are stdio.h, math.h,

string.h, andstdlib.h

stdio.hrelated functions:printf, scanf,etc math.hrelated functions: sin, cos, exp, pow,

sqrt, etc.

string.hrelated functions: strcmp, strcpy,strlen, etc.

stdlib.hrelated functions: abs, fabs


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Predefined Functions

(Library)-example#include #include #include

void main(){string name;int vol1, vol2, n, R, kTemp, length;

strcpy(name, Marina);vol2 = vol1 * exp(n * R * kTemp);length = strlen(Mahathir);

}


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User-Defined Functions What do we need to define and make

use of user-defined functions?

Function prototypes

Function definitions

Function calls


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Function Prototypes Function prototype is a declaration; indicates

the function exists

Should have function name, return type andparameter

Argument name is notcompulsory in functionheader

Function prototype hasthe following form: (arg_type arg_name, ...);

int sum (int num1,int num2);

int sum (int,int); //is also acceptablesemicolon


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Function Definitions Function definition includes the body of a function Function definition hasthe following form:

(arg_type arg_name, ...){

statements } int sum (int num1,int num2)

{int add;add = num1 + num2;return(add);}

Notice that argument name is used in the function body Unlike function prototype, argument name in function definition

mustbe included in function header

no semicolon

function header


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Function Calls Consists of a function name followed by an argument

expression list enclosed in parentheses

Function call hasthe following form: (exp, exp ...)

exp is an expressioncan be variable or constant

result = sum(x,y);


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EKT120: Computer Programming 13

Example of function in

program//This program sums up two numbers#include

int sum(int, int); //function prototype

int main()

{ int x,y, result;printf( Enter x and y : );

scanf(%d %d, &x, &y);

result = sum(x,y); //function call

printf(Sum is : %d, result);

return 0;

}

int sum(int num1, int num2)//function definition

{ int add;

add = num1+num2;

return(add);}

}

function header


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What about number, order

and type of parameter? Number, order and type of parameters in the

argument list of a function call and function

definition MUSTmatch. If function prototype and definition have three

parameters then the function call must havethree parameters.

If the types are int, floatand doublein the

prototype, the types in the function call shouldbe int, floatand double, respectively.


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What about number, order

and type of parameter?(e.g1)

Note that there are two arguments for function prototype,function definition and function call; the first is intand the

second is double. With these three we have met thenumber, order and type requirements.


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What about number, orderand type of parameter?(e.g2)

int sum(int, int); //function prototype

int sum(intnum1, intnum2) //function definition

sum(x,y); //function call

Refer to program in slide 13 Number, order and type parameter are met because:

there are two parameters, the parameters are listed inorder i.e respectively and first parameter is intandsecond parameter is int.


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Functions that do not return avalue

//This program sums up two numbers#include

voidsum_print(int, int); //function prototypevoid function1(); //function prototype

int main(){ int x,y;

function1(); //function callprintf(Enter x and y: );scanf(%d %d, &x, &y);sum_print(x,y); //function callreturn 0;

}voidsum_print(int num1, int num2)//function definition{ int add;

add = num1+num2;printf(Sum is: %d,add);

}voidfunction1(){ printf(Welcome to this program\n); }


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Functions that return a value

//This program sums up two numbers#include intsum(int,int); //function prototype

int main()

{ int x,y,result;

printf(Enter x and y: );

scanf(%d %d, &x, &y);

result = sum(x,y); //function callprintf(Sum is : %d,result);

return 0;

}

int sum(int num1, int num2) //function definition{ int add;

add = num1+num2;

return(add);}


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Miscellaneous about functions

Function call used as logical expressionint calc(int,int); //function prototypeint main(void)

{ int num1, num2;

scanf(%d %d,&num1,&num2);

if(calc(num1,num2)>100) //function call used as logical expressionprintf(result greater than 100);

else

printf(result less than 100);

return 0;

}

int calc(int n1,int n2)

{ int answer;

answer=n1+n2;

return(answer);

}


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Function call used inprintf statementint calc(int,int); //function prototypeint main(void)

{ int num1,num2;

scanf(%d %d,&num1,&num2);printf(Jawapan : %d,calc(num1, num2));//function callreturns a

//value and puts in printfreturn 0;

}

int calc(int n1,int n2){ int answer;

answer=n1+n2;

return(answer);

}


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Rules regarding naming convention for variables num1 passes value to n1, num2 passes value to n2 Better use different variable names for parameters in mainAND

parameters in function definition

int calc(int,int); //prototype functionint main(void){ int num1,num2,result; //declare like this

scanf(%d %d,&num1,&num2);result = calc(num1,num2); //function callprintf(jawapan : %d,result);return 0;

}

//function definitionint calc(int n1,int n2) //simply declare like this{ int answer;

answer=n1+n2;return(answer);

}


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Sample application

Write a C program that calculates and printsaddition and subtraction of numbers.

Your program should have functions: add : adds two numbers

subtract: subtracts two numbers

print_result: prints results from calculation


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Sample application(cont)#include int add(int,int);int subtract(int,int);void print_result(int);

int main()

{ int num1,num2,answer;char op;printf(Enter two numbers and operator:);scanf(%d %d %c, &num1,&num2,&op);switch(op){ case + :answer=add(num1,num2);break;

case - :answer=subtract(num1,num2);break;default: printf(Invalid operator);exit(0);

}

print_result(answer);return 0;

}

int add(int x,int y){

int sum;sum = x+y;return(sum);

}

int subtract(int x,int y){

int sub;sub=x-y;return(sub);

}

void print_result(int ans){

printf(Answer is %d, ans);}

1/* Fig. 5.4: fig05 04.c


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1. Function prototype

(3 parameters)

2. Function call

3. Function definition

Program Output

g g _

2 Finding the maximum of three integers */

3#include

4

5intmaximum(int, int, int); /* function prototype */

6

7intmain()

8{

9 inta, b, c;

10

11 printf( "Enter three integers: " );

12 scanf( "%d %d %d", &a, &b, &c );

13 printf( "Maximum is: %d\n", maximum( a, b, c ) );

14

15 return0;

16 }17

18 /* Function maximum definition */

19 intmaximum(intx, inty, intz)

20 {

21 intmax = x;

22

23 if( y > max )

24 max = y;25

26 if( z > max )

27 max = z;

28

29 returnmax;

30 }

Enter three integers: 22 85 17

Maximum is: 85


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Scope and Mechanics ofPassing Values to Functions

Scope refers to the region in which a declaration is active

File scope is also called global variable

declared at the top of a source file

declarations not placed in any functions

can be used by any statementsthat are being executedin the system

Function scope is also called local variable

declared in a block { } scope is within its blocklifetime while the block is

executed


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Global Variable : Example

#include

int global = 3; //This is the global variablevoid ChangeGlobal( );

int main(void){ printf("%d\n, global); //Reference to global

//variable in a functionChangeGlobal();

printf("%d\n", global);

return 0;}

void ChangeGlobal( ){ global = 5; } //Reference to global

//variable in a function


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Global Variable : Example

The output will be:

3

5


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Local Variable : Example #include

void ChangeLocal();

int main(void)

{ int local = 3; //This is a local variable

printf("%d\n", local); //Reference to local//variable in a function

ChangeLocal();printf("%d\n", local);

return 0;}

void ChangeLocal(){ int local = 5; //This is another local variableprintf("%d\n", local); }


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Local Variable : Example

The output will be:

3

5

3


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End Week 5Functions (1)

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EKT120_WEEK05_FUNCTIONS1