CP104 Introduction to Programming Top-down design with functions Lecture 6-8 __ 1 Top-Down Design...

CP104 Introduction to Programming Top-down design with functions Lecture 6-8 __ 1

Top-Down Design with Functions

• C Library functions• Case studies • Top-down design and structure charts

• Basic concepts about functions– Prototype, definition and function call– Input arguments– Output arguments– Void function and void argument– Actual parameter / formal parameter– Local variable

• Building programs from existing information


Reuse of Existing Code

• C has a rich function library consists many predefined functions.– What are they? arguments, output, and their data types.

• Use C library functions– To simply a program– To reduce the errors– To write program efficiently

• Example: mathematical function library – contains commonly used math function routines: ceil(x), cos(x),

exp(x), fabs(x), floor(x), log(x), log10(x), pow(x,y), sqrt(x), sin(x), tan(x)

– To include math library by adding #include <math.h>

– To call a math function


Case Study: Find the Roots of a Quadratic Equation ax2+bx+c = 0

• Problem– Get the coefficients a, b, and c.

Compute and display the roots of ax2+bx+c = 0

• Analysis– Input: a, b, c

– Output: root_1, root_2

– Relevant formulas

root_1 =

root_2 =

2 4

2

b b ac

a

2 4

2

b b ac

a


Find the Roots of a Quadratic Equation (Cont’d)

• Algorithm designAlgorithm 11. Get a, b, c2. Calculate root_1 = (-b + sqrt( pow(b,2) – 4*a*c ))/(2*a)3. Calculate root_2 = (-b - sqrt(pow(b,2) – 4*a*c ))/(2*a)4. Display root_1, root_2.

Algorithm 21. Get a, b, c2. Calculate the discriminant: disc = pow(b,2) – 4*a*c;

3. Calculate the square root of discriminant: sqrt_disc = sqrt(disc);

4. Calculate root_1 = (-b + sqrt_disc)/(2*a)5. Calculate root_2 = (-b – sqrt_disc)/(2*a)6. Display root_1, root_2

• Optimize the algorithm by reducing the number of operations. Tradeoff between space and time


Implementation: using existing math functions

#include <stdio.h>#include <math.h>

main(){ double a, b, c; double root_1, root_2; double disc, sqrt_disc;

printf("Enter the coefficients a, b, and c:\n"); scanf("%lf%lf%lf", &a, &b, &c);

disc = b*b - 4*a*c; sqrt_disc = sqrt(disc); /* sqrt() is a math function in math lib */ root_1 = (-b + sqrt_disc)/(2*a); root_2 = (-b - sqrt_disc)/(2*a);

printf("The roots of %fx^2 + %fx + %f = 0 are\nroot_1 = %f, root_2 = %f\n", a, b, c, root_1, root_2);

fflush(stdin); getchar();}


Case Study: Finding the Area and Circumferences of a Circle

• Problem– Get the radius of a circle. Compute and display the circle’s area and

circumference. • Analysis

– Input: radius– Output: area, circumference– Relevant formulas

• Problem constants: PI 3.14159• Area = PI * radius 2

• Circum = 2* PI * radius– Data requirements: double radius, area, circum

• Algorithm design1. Get the radius of a circle2. Calculate the area: area = PI * radius*radius3. Calculate the circumference: circum = 2*PI*radius4. Display the area and the circumference

• Implementation


Calculating the Area and the Circumference of a Circle


User Defined Function and Top-Down Design Method

• C allow a user to define a function. This makes th top-down design possible

• Top-down design_ a problem-solving method in which one first break a problem up into its major subproblems and then solve the subproblems to derive the solution to the original problem

• Structure chart __ a documentation tool that shows the relationships among the sub-problems of a problem.


Using Self-Defined Functions

#include <stdio.h>#define PI 3.14159

double area_circle(double);double circum_circle(double);

intmain(void){ double radius; /*input - radius of a circle */ double area; /* output - area of a circle */ double circum; /* output - circumference */

/* Get the circle radius */ printf("Enter radius> "); scanf("%lf", &radius);

area = area_circle(radius);

circum = circum_circle(radius);

/* Display the area and circumference */ printf("The area is %.4f\n", area); printf("The circumference is %.4f\n", circum); return 0;}

/* Calculate the area */double area_circle(double r){ return(PI * r * r);}

/* Calculate the circumference */double circum_circle(double r){ return(2*PI *r);}


Structured Programming

• A program in which individual program tasks are performed by independent section of program code

• Advantages– Easier to write structured program become complex

programming problems are broken into a number of smaller and simpler taskes

– Easier to debug, i.e., easier to isolate a bug to a specific section of code

– Code reuse, functions in one program can be used in another program for the same task

• With functions top-down design method can be applied to write structured program.


Case study: Draw a Simple Diagram

Decomposition of the figure

• Draw a circle

• Draw a intersecting lines

• Draw a base line


Structure Chart for Drawing a Stick Figure


Function Prototypes and Main Function for Stick Figure


Function draw_circle


Function draw_triangle


Program to Draw a Stick Figure


Program to Draw a Stick Figure (cont’d)


Flow of Control Between the main Function and a Function Subprogram


Case Study: Multiply two Numbers (floating)

#include <stdio.h>/* function prototype */ void printMessage(void); double multiply(double, double);

int main(void){ double a, b, c; printMessage(); scanf(“%lf %lf”,&a,&b);

c = multiply(a,b); printf(“%f”, c);}

/* definition of function multiply */void printMessage(){ printf(“Input two numbers:\n”);}

double multiply(double x, double y){ double z; z = x * y; return(z);}

#include <stdio.h>

/* definition of function multiply */

void printMessage(){ printf(“Input two numbers:\n”);}

double multiply(double x, double y){ double z; z = x * y; return(z);}

main(void){ double a, b, c; printMessage(); scanf(“%lf %lf”,&a,&b);

c = multiply(a,b); printf(“%f”, c);}

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CP104 Introduction to Programming Top-down design with functions Lecture 6-8 __ 1 Top-Down Design...

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