chapter 3-b.pdf

User-defined functions

GENG 200 Marwan Alakhras

1

Functions has the following effects on your program

1. Prototype : necessary for calling (model for calling)

2. Definition: head and body, to perform the specific task

3. Calling : (invoking) using the function to carry on the task

The above classification is not the only valid one.

example1


2

Do you remember this

“Write a C program to solve the problem of converting

Fahrenheit temperature to Celsius”

Analysis

Input : Ftemp

Output Ctemp

Process

Ctemp=5/9(Ftemp-32)

Solution


3

Solution with New Structure(with functions)

GENG200 Marwan Alakhras

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1. /* program structure */

2. #include <stdio.h>

3. double feh_to_cel(double); // Prototype ;

4. int main() /*function main begins program execution */

5. { double feh,cel;

6. scanf("%lf",&feh);

7. cel = feh_to_cel(feh); // calling ;

8. printf("\n result = %6.1f", cel);

9. return 0; /*indicate that program ended successfully*/

10.} /* end program function main */

Ma

in B

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11.double feh_to_cel(double a) /*function header */

12.{ double m; /*local variable */

13. m = (5.0/9.0)*(a-32);

14. return m; /* sends result back to cel in main line 7*/

15.} /* end function feh_to_cel*/

fun

ctio

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prototypes


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Prototype : model necessary for calling

It must be written before main program

It contains the following items 1. Return data type (int, double, char, or void for nothing)

2. Function name ( valid according to the rules), followed by ( )

3. Parameters list, inside ( )

1. How many

2. Type for each

3. Order

4. Names for every one (optional)

5. If there no parameter, then void

4. End with Semicolon ( ; )

Examples int fun(int a);

double xx(int a, double y, char);

void fun(char m, int x);

void f16(void);

double hi_m(void);

General Format:

Return_type f_name(parameter_list);

Function Definitions

Function definitions contains

Head (prototype, without semicolon ; )

Body (begins with { , and ends with } )

Return expression;

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Marwan Alakhras

return-value-type function-name( parameter-list )

{

declarations and statements;

return expression;

}

Example double feh_to_cel(double a) /*function header */

{

double m; /*local variables */

m = (5.0/9.0)*(a-32); /* calculation statement */

return m; /* sends result back to the caller program */

} /* ends function */

Function Definitions

Definitions must occur after main body

Definitions and statements: function body (block)

Variables can be defined inside blocks (can be nested)

Variables declared inside the function can be used only inside function

Functions cannot be defined inside other functions

Returning control

If nothing returned

return;

or, until reaches right brace }

If something returned

return expression;

The expression in the return statement can be variable, constant, value, or function

But it must match the return-type

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Marwan Alakhras

calling


8

Functions with are not used unless they are called In this course Function calling must occur within main function body or

other function body (no recursion) Calling occur according to the prototype or function header Functions are called with name and correct parameters list

Correct Name Correct Arguments lists and values

Name, order, type for each

Examples (according to the previous slide function)

double x = feh_to_cel(100.0);

temp2 = feh_to_cel(temp1);

Result = 1/temp1 + feh_to_cel(30 + temp1/80.0);

printf(“%6.2f”, feh_to_cel(temp1));

Result = pow(feh_to_cel(temp2), 3);

Calling (continue)


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If the function has no return result (void)

Then calling must be alone on the line

Examples 1. void xx(int, double);

2. void yy(void);

Then the calling statements are respectively 1. xx(3,5.5);

2. yy();

Function Prototypes

Function prototype Function name

Parameters – what the function takes in

Return type – data type function returns (default int)

Used to validate functions

Prototype only needed if function definition comes after use in program

The function with the prototype

int maximum( int x, int y, int z );

Takes in 3 ints

Returns an int (single result)

Promotion rules and conversions Converting to lower types can lead to errors

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Marwan Alakhras

Example 2


11

Based on example 3.3 page 142,

Modify the program to have function side3, which receives values for b, c, and angle α in RAD, then returns the third side length value as:

a2=b2+c2 - 2bc.cos(α)

Solution


12

1. #include<stdio.h>

2. #include<math.h>

3. #define bi 22.0/7.0

4. double side3(double x, double y, double angle);

5. int main(){

6. double a,b,c,alpha;

7. printf("\n Enter values for two sides and angle"

8. "\nbetween them in Deg : ");

9. scanf("%lf%lf%lf",&b,&c,&alpha);

10. a=side3(b,c,alpha*bi/180);

11. printf("\nThe third side is %.2f \n",a);

12. return 0;

13. }

14. double side3(double x, double y, double angle){

15. return sqrt(pow(x,2)+pow(y,2)-2*x*y*cos(angle));

16. }

Output screen


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Enter values for two sides and angle

between them in Deg : 3 4 90

The third side is 5.00

Example 3


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Modify the previous example2 by adding another function GET_data(); to get the data from the user one by one;

Hint: this function should have no arguments, but returned value

solution


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1.#include<stdio.h>

2.#include<math.h>

3.#define bi 22.0/7.0

4.double side3(double x, double y, double angle);

5.double GET_data(void);

6.int main(){


8. printf("\nEnter values for two sides and angle "


10. b=GET_data();

11. c=GET_data();

12. alpha=GET_data();


14. printf("\n The third side is %.2f \n",a);

15. return 0;

16.}

Solution (continue)


16



19. }

20. double GET_data(void){

21. double x;

22. scanf("%lf",&x);

23. return x;

24. }




Example 4


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Modify the last program (example3) by adding another function DISPLAY to show the final result on the screen

solution


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1.#include<stdio.h>

2.#include<math.h>

3.#define bi 22.0/7.0

4.double side3(double x, double y, double angle);

5.double GET_data(void);

6.void DISPLAY(double);

7.int main(){


9. printf("\nEnter values for two sides and angle "


11. b=GET_data();

12. c=GET_data();

13. alpha=GET_data();


15. DISPLAY(a);

16. return 0;

17.}

Solution (continue)


19



20. }

21. void DISPLAY(double x){

22. printf("\n The third side is %.2f \n",x);

23. }

24. double GET_data(void){

25. double x;

26. scanf("%lf",&x);

27. return x;

28. }




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