1. Computer Programming w/ Eng. Applications
CS 2073
Computer Programming w/ Eng. Applications
Ch 2
Simple C Programs
Turgay Korkmaz
Office: SB
Phone: (210)
Fax: (210)
web:

2. Name
Addr
Content
Lecture 3
Lecture++;

3. 2.1 Program Structure

4. { } /*-----------------------------------------*/ Comments
/* Program chapter1_ */
/* 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);
return 0; /* Exit program. */ }
Comments
Preprocessor,
standard C library
every C program must have main function, this one takes no parameters and it returns int value
{  begin
Variable declarations, initial values (if any)
Statements
must end with ;
indentation
return 0
}  end of function

5. General Form
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
preprocessing directives
int main(void) {
declarations
statements }

6. Another Program /***************************************************/
/* Program chapter */
/* This program computes the sum of two numbers */
#include <stdio.h>
int main(void) {
/* Declare and initialize variables. */
double number1 = , number2 = 45.7, sum;
/* Calculate sum. */
sum = number1 + number2;
/* Print the sum. */
printf(“The sum is %5.2f \n”, sum);
system("pause"); /* keep DOS window on the screen*/
return 0; /* Exit program. */ }
/****************************************************/

7. 2.2 Constants and Variables
What is a variable in math?
f(x) = x2+x+4
In C,
A variable is a memory location that holds a value
An identifier or variable name is used to reference a memory location.

8. Memory double x1=1,x2=7,distance; 1 = 00000001 7 = 00000111
name
address
Memory - content … 11 12 13 14 15 16
1 =
7 =
? =
How many memory cells does your computer have?
Say it says 2Gbyte memory?
1K= or 210 = 1024
1M=106 or 220 = 10242
1G= or 230 = 10243 x1 x2
distance

9. Memory Snapshot Name Addr Content x1 1 y1 5 x2 4 y2 7 side_1 ? side_2
distance

10. Rules for selecting a valid identifier (variable name)
Must begin with an alphabetic character or underscore (e.g., abcABC_)
May contain only letters, digits and underscore (no special characters
Case sensitive (AbC, aBc are different)
Cannot use C keywords as identifiers (e.g., if, case, while)

11. Are the following valid identifiers?
initial_time
DisTaNce
X&Y
distance 1x
x_1
rate%
x_sum
switch

12. C Numeric Data Types

13. Example Data-Type Limits

14. C Character Data Type: char
char result =‘Y’;
In memory, everything is stored as binary value, which can be interpreted
as char or integer. Examples of ASCII Codes

15. Memory
name
address
Memory - content
How to represent ‘a’ ?
char My_letter=‘a’;
int My_number = 97
Always we have 1’s and 0’s in the memory. It depends on how you look at it?
For example, 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? 1 2 3 4 5 6 …
‘a’=
97 =
? =
My_letter
My_number

16. Program to Print Values as Characters and Integers

17. Constants
A constant is a specific value that we use in our programs. For example
3.14, 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; ?
2.0 a b
area
circumference r

18. Symbolic Constants What if you want to use a better estimate of ?
For example, you want instead of 3.14.
You need to replace all by hand 
Better solution, define  as a symbolic constant, e.g.
#define PI …
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

19. 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 3
char ch;
ch = ‘a’; 5
‘a’
sum x ch

20. Assignment examples (cont’d)
int x, y, z;
x = y = 0;
right to left!
Z = 1+1;
Example 4
y=z;
y=5; x y z 2 2 5

21. 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 2 a b c
5.0
long double, double, float, long integer, integer, short integer, char
Data may be lost. Be careful!
 No data loss

22. Exercise: swap
Write a set of statements that swaps the contents of variables x and y x 3 x 5 y 5 y 3
Before
After

23. Exercise: swap First Attempt x=y; y=x; After x=y 5 x y After y=x 5 x y3 5 x y
Before

24. Exercise: swap Solution temp= x; x=y; y=temp; after temp=x after x=y
after y = temp 3
temp 5 x y ?
temp 3 5 x y
Before
Will the following solution work, too? temp= y;
y=x;
x=temp;
Write a C program to swap the values of two variables

25. Name
Addr
Content
Lecture 4
Lecture++;

26. 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

27. 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 X 5

28. 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 1
int 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 1.666
double B=3.0/6.0;  B will have the value of 0.5

29. Implement a program that computes/prints simple arithmetic operations
Declare a=2, b=5, c=7, d as int Declare x=5.0, y=3.0, z=7.0, w as double d = c%a Print d d = c/a Print d w = z/x Print w d = z/x Print d w = c/a Print w a=a+1 Print a … try other arithmetic operations too..

30. Mixed operations and Precedence of Arithmetic Operators
int a=4+6/3*2;  a=?
int b=(4+6)/3*2;  b=?
a= 4+2*2 = 4+4 = 8
b= 10/3*2 = 3*2= 6
assign = Right to left

31. Extend the previous program to compute/print mixed arithmetic operations
Declare a=2, b=5, c=7, d as int
Declare x=5.0, y=3.0, z=7.0, w as double
d = a+c%a Print d
d = b*c/a Print d
w = y*z/x+b Print w
d = z/x/y*a Print d
w = c/(a+c)/b Print w
a=a+1+b/3 Print a
… try other arithmetic operations too..

32. 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

33. 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 wrong
x=x*(4+2/3) correct

34. Precedence of Arithmetic Operators (updated)

35. Writing a C statement for a given MATH formula
Area of trapezoid
area = base*(height1 + height2)/2;
How about this

36. Exercise Tension = 2*m1*m2 / (m1 + m2) * g
wrong
Tension = 2*m1*m2 / (m1 + m2) * g
Write a C statement to compute the following
f = (x*x*x-2*x*x+x-6.3)/(x*x+0.05*x+3.14);

37. Exercise: Arithmetic operations? 5 a b c x y
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.
a = 12 b = 3 c= 5 x = y =

38. 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);

39. Step-by-step show how C will perform the operations
output:
Value of c = 27

40. Step-by-step show how C will perform the operations
int a = 8, b = 10, c = 4;
c = a % 5 / 2 + -b / (3 – c) * 4 + a / 2 * b;
printf("New value of c is %d \n", c);

41. Exercise: reverse a number
Suppose you are given a number in the range [ ]
Write a program to reverse it
For example,
num is 258
reverse 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;

42. Name
Addr
Content
Lecture 5
Lecture++;

43. 2.4 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>

44. 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 = degrees
Conversion Specifier
Control String
Identifier

45. Conversion Specifiers for Output Statements
Frequently Used

46. Standard Output Output of -145 Output of 157.8926 Specifier
Value Printed %i
-145
%4d
%3i
%6i
__-145
%-6i
-145__
%8i
____-145
%-8i
-145____
Specifier
Value Printed %f
%6.2f
157.89
%7.3f
%7.4f
%7.5f %e
e+02
%.3E
1.579E+02

47. Exercise int sum = 65; double average = 12.368; char ch = ‘b’;
Show the output line (or lines) generated by the following statements.
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);

48. Exercise (cont’d) Solution Sum = 65; Average = 12.4 Sum = 65
Sum and Average
Character is b; Sum is A
Character is 98; Sum is 65

49. 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

50. Conversion Specifiers for Input Statements
Frequently Used

51. Exercise int i; scanf(“%f %i“, &f, &i);
float 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 1 12 1

52. 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?

53. 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);

54. Programming exercise
Write a program  that asks user to enter values for the double variables (a, b, c, d) in the following formula. It then computes the result (res) and prints it with three digits after .

55. Exercise
Study Section 2.5 and 2.6 from the textbook

56. Name
Addr
Content
Lecture 6
Lecture++;

57. Library Functions

58. 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.

59. 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,
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 [-, ].

60. 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
theta = 60;
theta_rad = theata * PI / 180;
b = sin(theta_rad); /* is not the same as sin(theta); */

61. Exercise velocity = sqrt(vo*vo+2*a*(x-xo));
Write an expression to compute velocity using the following equation
Assume that the variables are declared
velocity = sqrt(vo*vo+2*a*(x-xo));
velocity = sqrt(pow(vo,2)+2*a*(x-xo));

62. Exercise center = (38.19*(pow(r,3)-pow(s,3))*sin(a))/
Write an expression to compute velocity using the following equation
Assume that the variables are declared
Make sure that a is given in radian; otherwise, first convert it to radian
center = (38.19*(pow(r,3)-pow(s,3))*sin(a))/
((pow(r,2)-pow(s,2))*a);
center = (38.19*(r*r*r - s*s*s)*sin(a))/((r*r –s*s)*a);

63. Exercise: Compute Volume
Write a program to compute the volume of a cylinder of radius r and height h r h

64. Solution: Compute Volume
Problem Solving Methodology
1. Problem Statement
2. Input/Output Description
3. Hand Example
4. Algorithm Development
5. Testing

65. Solution: Compute Volume (cont’d)
Problem Statement
compute the volume of a cylinder of radius r and height h
Input Output Description
radius r
volume v
height h

66. 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)

67. Solution: Compute Volume (coding)
#include <stdio.h>
#define PI
int main(void) {
/* Declare Variables */
double radius, height, volume;
printf("Enter radius: "); scanf("%lf",&radius);
printf("Enter height: "); scanf("%lf",&height);
/* Compute Volune */
volume = PI*radius*radius*height;
/* Print volume */
printf("Volume = %8.3f \n", volume);
system("pause");
exit(0); }

68. Exercise
Write a program to find the radius of a circle given its area. Read area from user. Compute radius and display it. r

69. Exercise
Write a program that asks user to enter A in degrees, a and b in cm, then computes
B=? in degrees
C=? in degrees
c=? in cm
area=? in cm2 A B C a b c
For example, given A=36o, a=8 cm, b=5 cm:
B=21.55o, C=122.45o, c=11.49 cm

70. Write a program that finds the intersection of two lines and the angle between them
See handout
A1x+B1y+C1=0
A2x+B2y+C2=0

71. 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.

72. Exercise What 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); }

73. Skip
Study Section 2.9 from the textbook
Skip Section 2.10