1 Original Author : Turgay Korkmaz e-mail: [email protected] web: korkmazkorkmaz Revised for ME2008 Spring—(2009_ME2008a_C.

1

Original Author : Turgay Korkmaz

e-mail: [email protected]: www.cs.utsa.edu/~korkmaz

Revised for ME2008 Spring—(2009_ME2008a_C ( NTUST.ME)

CS 2073Computer Programming w/

Eng. Applications – (ch2)

Simple C Programs

2

Program Structure

3

Thinking : Q1

1. Problem statement Compute the straight line distance between two points in a

plane2. Input/output descriptionPoint 1 (x1, y1)

Point 2 (x2, y2)Distance between two points (distance)

(x1,y1)

(x2, y2)

URL Source: http://www.cs.utsa.edu/~korkmaz/teaching/cs2073/ ( Ch1).

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3. Hand example

Example Q1 (cont’d)

22 side2side1distance

22 23distance

22 side2side1distance

61.313distance

side1 = 4 - 1 = 3 side2 = 7 - 5 = 2

5

Example 1 (cont’d)

4. Algorithm development and codinga. Generalize the hand solution and list/outline the

necessary operations step-by-step1) Give specific values for point1 (x1, y1) and point2

(x2, y2) 2) Compute side1=x2-x1 and side2=y2-y13) Compute 4) Print distance

b. Convert the above outlined solution to a program using any language you want (see next slide for C imp.)

22 side2side1distance

6

Example 1 (cont’d)

7

Example 1 (cont’d)

5. Testing After compiling your program, run

it and see if it gives the correct result.

Your program should print outThe distance between two points is 3.61

If not, what will you do?

8

Modification to Example 1

x1=2, y1=5, x2=10, y2=8,

How will you find the distance between two other points (2,5) and (10,8)?

9

/*-----------------------------------------*//* Program chapter1_1 *//* This program computes the *//* distance between two points. */

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

int main(void){ /* Declare and initialize variables. */ double x1=1, y1=5, x2=4, y2=7,

side_1, side_2, distance;

/* Compute sides of a right triangle. */ side_1 = x2 - x1; side_2 = y2 - y1; distance = sqrt(side_1*side_1 + side_2*side_2);

/* Print distance. */ printf("The distance between the two points is " "%5.2f \n",distance);

/* Exit program. */ system("pause"); return 0;}/*-----------------------------------------*/

Comments

Preprocessor, standard C library

main function: No parameters, return type is int

{ begin

Variable declarations, initial values

Statements

indentation

indentation

return 0

} end of function

10

General Form

preprocessing directives

int main(void)

{

declarations

statements

}

The main function contains two types of commands: declarations and statements

Declarations and statements are required to end with a semicolon (;)

Preprocessor directives do not end with a semicolon

To exit the program, use a return 0; statement

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Another Program/***************************************************//* Program chapter1 *//* This program computes the sum of two numbers */

#include <stdio.h>int main(void){ /* Declare and initialize variables. */ double number1 = 473.91, number2 = 45.7, sum;

/* Calculate sum. */ sum = number1 + number2;

/* Print the sum. */ printf(“The sum is %5.2f \n”, sum);

/* Exit program. */ return 0;}/****************************************************/

12

2.2 Constants and Variables A variable is a memory location

that is assigned a name or an identifier

An identifier is used to reference a memory location.

Memorysnapshot

13

Memory

1 = 00000001

7 = 00000111

? = 01001101

0

1

2

3

4

5

6

…

x1

x2

distance

addressname Memory - content

How many memory cells does your computer have?

Say it says 2Gbyte memory?

1K=103 or 210 = 1024

1M=106 or 220 = 10242

1G=109 or 230 = 10243

14

Rules for selecting a valid identifier (variable name)

Must begin with an alphabetic character or underscore

May contain only letters, digits and underscore (no special characters)

Case sensitive Can not use keywords as identifiers

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Are the following Valid Identifiers?

distance 1x x_1

rate%x_sumswitch

initial_timeDisTaNceX&Y

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C Numeric Data Types

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Example Data-Type Limits

18

C Character Data Type: char

In memory, everything is stored as binary value, which can be interpreted as char or integer. Examples of ASCII Codes

char result =‘Y’;

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MemoryHow to represent ‘a’ ?

char My_letter=‘a’;

int My_number = 97

Always we have 1’s and 0’s in the memory, it depends how you look at it?

For example, 01100001 is

97 if you look at it as int, or

‘a’ if you look at it as char

‘3’ is not the same as 3

How to represent 2.5?

‘a’= 01100001

97 = 01100001

? = 01001101

0

1

2

3

4

5

6

…

My_number

address name Memory - content

My_letter

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Program to Print Values as Characters and Integers

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Constants A constant is a specific value that we use

in our programs. For example3.14, 97, ‘a’, or “hello”

In your program,int a = 97;char b =‘a’;double area, r=2.0;double circumference;area = 3.14 * r*r;circumference = 2 * 3.14 * r;

01100001

01100001

?

?

2.0

a

b

areacircumference

r

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Symbolic Constants What if you want to use a better estimate of ?

For example, you want 3.141593 instead of 3.14. You need to replace all by hand Better solution, define as a symbolic constant,

e.g.#define PI 3.141593…area = PI * r * r;circumference = 2 * PI * r;

Defined with a preprocessor directive Compiler replaces each occurrence of the directive

identifier with the constant value in all statements that follow the directive

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2.3 Assignment Statements

Used to assign a value to a variable General Form:

identifier = expression;

/* ‘=‘ means assign expression to identifier */ Example 1

double sum = 0; Example 2

int x;x=5;

Example 3char ch;ch = ‘a’;

0

5

‘a’

sum x

ch

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Assignment examples (cont’d) Example 3

int x, y, z;x = y = 0;right to left!Z = 1+1;

Example 4y=z;

y=5;

0

0

2

x

y

z

2 5

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Assignment examples with different types

int a, b=5;double c=2.3;…a=c; /* data loss */c=b; /* no data loss

*/

?

5

2.3

a

b

c

2

5.0

long double, double, float, long integer, integer, short integer, char

Data may be lost. Be careful!

No data loss

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Arithmetic Operators Addition + sum = num1 + num2; Subtraction - age = 2007 – my_birth_year; Multiplication * area = side1 * side2; Division / avg = total / number; Modulus % lastdigit = num % 10;

Modulus returns remainder of division between two integers

Example 5%2 returns a value of 1 Binary vs. Unary operators

All the above operators are binary (why) - is an unary operator, e.g., a = -3 * -4

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Arithmetic Operators (cont’d)

Note that ‘id = exp‘ means assign the result of exp to id, so

X=X+1 means first perform X+1 and Assign the result to X

Suppose X is 4, and We execute X=X+1

4 X5

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Integer division vs Real division Division between two integers results in

an integer. The result is truncated, not rounded Example:

int A=5/3; A will have the value of 1int B=3/6; B will have the value of 0

To have floating point values:double A=5.0/3; A will have the value of

1.666double B=3.0/6.0; B will have the value of 0.5

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Precedence of Arithmetic OperatorsMixed operations:

int a=4+6/3*2; a=?

int b=(4+6)/3*2; b=?

a= 4+2*2 = 4+4 = 8b= 10/3*2 = 3*2= 6

5 assign = Right to left

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Exercise Compute the following

2*(3+2) 2*3+2 6-3*2

Area of trapezoid

area = 1.0/2*base*(height_1+height_2);

2

)(* 21 heightheightbasearea

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Exercise Write a C statement to compute the

following

14.305.0

3.622

23

xx

xxxf

f = (x*x*x-2*x*x+x-6.3)/(x*x+0.05*x+3.14);

gmm

mmTension

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212 Write a C statement to compute the

following

Tension = 2*m1*m2 / m1 + m2 * g;

Tension = 2*m1*m2 / (m1 + m2) * g

Wrong !!

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Increment and Decrement Operators

Increment Operator ++ post increment x++; pre increment ++x;

Decrement Operator --

post decrement x--; pre decrement --x;

}x=x+1;

}x=x-1;

But, the difference is in the following example. Suppose x=10;

A = x++ - 5; means A=x-5; x=x+1; so, A= 5 and x=11

B =++x - 5; means x=x+1; B=x-5; so, B=6 and x=11

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Abbreviated Assignment Operator

operator example equivalent statement += x+=2; x=x+2;-= x-=2; x=x-2;*= x*=y; x=x*y;/= x/=y; x=x/y;%= x%=y; x=x%y;

!!! x *= 4+2/3 x = x*4+2/3 wrongx=x*(4+2/3)

correct

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Precedence of Arithmetic Operators (updated)

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Exercise: swap Write a set of statements that swaps

the contents of variables x and y

3 5

x y

5 3

x y

Before After

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Exercise: swapFirst Attempt

x=y;y=x;

3 5

x y

5 5

x y

Before After x=y

5 5

x y

After y=x

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Exercise: swapSolution

temp= x;x=y;y=temp;

3 5

x y

Before

?

temp

3 5

x y

after temp=x

3

temp

5 5

x y

after x=y

3

temp

5 3

x y

after y = temp

3

temp

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Exercise: reverse a number

Suppose you are given a number in the range [100 999]

Write a program to reverse it For example,

num is 258reverse is 852

int d1, d2, d3, num=258, reverse;

d1 = num / 100;

d2 = num % 100 / 10;

d3 = num % 10;

reverse = d3*100 + d2*10 + d1;

printf(“reverse is %d\n”, reverse);

d1 = num / 100;d3 = num % 10;reverse = num – (d1*100+d3) + d3*100 + d1;

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Exercise: Arithmetic operations

Show the memory snapshot after the following operations by hand

int a, b, c=5; double x, y; a = c * 2.5; b = a % c * 2 - 1; x = (5 + c) * 2.5; y = x – (-3 * a) / 2; Write a C program and print out the values

of a, b, c, x, y and compare them with the ones that you determined by hand.

?

?

5

?

?

a

b

c

x

y

a = 12 b = 3 c= 5 x = 25.0000 y = 43.0000

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Exercise: Arithmetic operations

Show how C will perform the following statements and what will be the final output?

int a = 6, b = -3, c = 2;

c= a - b * (a + c * 2) + a / 2 * b;

printf("Value of c = %d \n", c);

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Step-by-step show how C will perform the operations

c = 6 - -3 * (6 + 2 * 2) + 6 / 2 * -3; c = 6 - -3 * (6 + 4) + 3 * -3 c = 6 - -3 *10 + -9 c = 6 - -30 + -9 c = 36 + -9 c = 27 output:

Value of c = 27

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Standard Input and Output Output: printf Input: scanf

Remember the program computing the distance between two points!

/* Declare and initialize variables. */ double x1=1, y1=5, x2=4, y2=7, side_1, side_2, distance; How can we compute distance for different points? It would be better to get new points from user, right?

For this we will use scanf To use these functions, we need to use

#include <stdio.h>

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Standard Output printf Function

prints information to the screen requires two arguments

control string Contains text, conversion specifiers or both

Identifier to be printed Example

double angle = 45.5;printf(“Angle = %.2f degrees \n”, angle);

Output:Angle = 45.50 degrees

Control String

Identifier

Conversion Specifier

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Conversion Specifiers for Output Statements

Frequently Used

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Standard Output

Output of -145 Output of 157.8926

Specifier Value Printed

%f 157.892600

%6.2f 157.89

%7.3f 157.893

%7.4f 157.8926

%7.5f 157.89260

%e 1.578926e+02

%.3E 1.579E+02

Specifier

Value Printed

%i -145

%4d -145

%3i -145

%6i __-145

%-6i -145__

%8i ____-145

%-8i -145____

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Exercise

printf("Sum = %5i; Average = %7.1f \n", sum, average);

printf("Sum = %4i \n Average = %8.4f \n", sum, average);

printf("Sum and Average \n\n %d %.1f \n", sum, average);

printf("Character is %c; Sum is %c \n", ch, sum);

printf("Character is %i; Sum is %i \n", ch, sum);

int sum = 65;

double average = 12.368;

char ch = ‘b’;

Show the output line (or lines) generated by the following statements.

47

Exercise (cont’d) Solution

Sum = 65; Average = 12.4

Sum = 65

Average = 12.3680

Sum and Average

65 12.4

Character is b; Sum is A

Character is 98; Sum is 65

48

Standard Input scanf Function

inputs values from the keyboard required arguments

control string memory locations that correspond to the specifiers in

the control string Example:

double distance;char unit_length;scanf("%lf %c", &distance, &unit_length);

It is very important to use a specifier that is appropriate for the data type of the variable

49

Conversion Specifiers for Input Statements

Frequently Used

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Exercisefloat f;int i;scanf(“%f %i”,&f,&i);

What will be the values stored in f and i after scanf statement if following values are entered

12.5 112 4512 23.212.1 10121

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Good practice You don’t need to have a printf before

scanf, but it is good to let user know what to enter:printf(“Enter x y : ”);scanf(“%d %d”, &x, &y);

Otherwise, user will not know what to do!

What will happen if you forget & before the variable name?

52

Exercise: How to input two points without re-compiling the program

printf(“enter x1 y1: “);

scanf(“%lf %lf“, &x1, &y1);

printf(“enter x2 y2: “);

scanf(“%lf %lf“, &x2, &y2);

53

Skip

Study Section 2.5 and 2.6 from the textbook

54

Library Functions

55

2.7 Math Functions#include <math.h>

fabs(x) Absolute value of x.

sqrt(x) Square root of x, where x>=0.

pow(x,y) Exponentiation, xy. Errors occur if x=0 and y<=0, or if x<0 and y is not an integer.

ceil(x) Rounds x to the nearest integer toward (infinity). Example, ceil(2.01) is equal to 3.

floor(x) Rounds x to the nearest integer toward - (negative infinity). Example, floor(2.01) is equal to 2.

exp(x) Computes the value of ex.log(x) Returns ln x, the natural logarithm of x to the base e.

Errors occur if x<=0.log10(x) Returns log10x, logarithm of x to the base 10.

Errors occur if x<=0.

56

Trigonometric Functions

sin(x) Computes the sine of x, where x is in radians.cos(x) Computes the cosine of x, where x is in radians

tan(x) Computes the tangent of x, where x is in radians.asin(x)Computes the arcsine or inverse sine of x,

where x must be in the range [-1, 1]. Returns an angle in radians in the range [-/2,/2].

acos(x) Computes the arccosine or inverse cosine of x,

where x must be in the range [-1, 1].Returns an angle in radians in the range [0, ].

atan(x) Computes the arctangent or inverse tangent of x. The Returns an angle in radians in the range [-/2,/2].

atan2(y,x) Computes the arctangent or inverse tangent of the value y/x. Returns an angle in radians in the range [-, ].

57

Parameters or Arguments of a function A function may contain no argument or contain

one or more arguments If more than one argument, list the arguments

in the correct order Be careful about the meaning of an argument.

For example, sin(x) assumes that x is given in radians, so to compute the sin of 60 degree, you need to first conver 60 degree into radian then call sin function:#define PI 3.141593theta = 60;theta_rad = theata * PI / 180;b = sin(theta_rad); /* is not the same as sin(theta);

*/

58

Exercise Write an expression to compute velocity using the

following equation Assume that the variables are declared

)(22 xoxavovelocity

velocity = sqrt(vo*vo+2*a*(x-xo));

59

Exercise Write an expression to compute velocity using the

following equation Assume that the variables are declared

asr

asrcenter

)(

sin)(19.3822

33

center = (38.19*(pow(r,3)-pow(s,3))*sin(a))/ ((pow(r,2)-pow(s,2))*a);

60

Exercise: Compute Volume Write a program to compute the volume

of a cylinder of radius r and height h

hrV 2

h

r

61

Solution: Compute Volume

Problem Solving Methodology

1. Problem Statement

2. Input/Output Description

3. Hand Example

4. Algorithm Development

5. Testing

62

Solution: Compute Volume (cont’d) Problem Statement

compute the volume of a cylinder of radius r and height h

Input Output Description

radius

height

volume

63

Solution: Compute Volume (cont’d) Hand example

r=2, h =3, v=37.68 Algorithm Development

Read radius Read height Compute Volume Print volume

Convert to a program (see next slide)

hrV 2

64

Solution: Compute Volume (cont’d)#include <stdio.h>

#define PI 3.141593

int main(void){ /* Declare Variables */ double radius, height, volume;

/* Get Radius from Keyboard */ printf("Enter radius: \n"); scanf("%lf",&radius);

/* Get Height from Keyboard */ printf("Enter height: \n"); scanf("%lf",&height);

/* Compute Volune */ volume = PI*radius*radius*height;

/* Print volume */ printf("Volume = %8.3f \n",volume);

/* exit program */ system("pause"); exit(0);}

65

Exercise Write a program to find the radius of a

circle given its area. Read area from user. Compute radius and display it.

2rA

r

66

2.8 Character Functions#include <ctype.h>

putchar(‘a’);C= getchar();

toupper(ch) If ch is a lowercase letter, this function returns the corresponding uppercase letter; otherwise, it returns ch

isdigit(ch) Returns a nonzero value if ch is a decimal digit; otherwise, it returns a zero.

islower(ch) Returns a nonzero value if ch is a lowercase letter; otherwise, it returns a zero.

isupper(ch) Returns a nonzero value if ch is an uppercase letter; otherwise, it returns a zero.

isalpha(ch) Returns a nonzero value if ch is an uppercase letter or a lowercase letter; otherwise, it returns a zero.

isalnum(ch) Returns a nonzero value if ch is an alphabetic character or a numeric digit; otherwise, it returns a zero.

67

ExerciseWhat is the output of the following program

#include <stdio.h>#include <ctype.h>

int main(void){ char ch1='a', ch2; char ch3='X', ch4; char ch5='8';

ch2 = toupper(ch1); printf("%c %c \n",ch1,ch2); ch4 = tolower(ch3); printf("%c %c \n",ch3,ch4);

printf("%d\n",isdigit(ch5)); printf("%d\n",islower(ch1)); printf("%d\n",isalpha(ch5));

system("pause"); return(0);}