1. Engineering Problem Solving with C
CSCI-125/ENGR-144
Engineering Problem Solving with C
Ch 2

2. 2.1 Program Structure

3. { } /*-----------------------------------------*/ 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

4. 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 }

5. 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. */ }
/****************************************************/

6. 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.

7. 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

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

9. 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)

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

11. C Numeric Data Types

12. Example Data-Type Limits

13. 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

14. 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 1 2 3 4 5 6 …
‘a’=
97 =
? =
My_letter
My_number

15. Program to Print Values as Characters and Integers

16. 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

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. 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

26. 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

27. 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

28. 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..

29. Exercise int a=27, b=6, c; c = b%a; 2. int a=27, b=6; float c;
c = a/(float)b;
3. int a; float b=6, c=18.6;
a = c/b;
4. int b=6; float a, c=18.6;
a = (int)c/b;

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. 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>

42. 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

43. Conversion Specifiers for Output Statements
Frequently Used

44. 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

45. Special Characters \n newline each escape sequence
\t tab represents only one
\b backspace character
\\ backslash
\? Question mark
\’ Single quote
\” Double quote
/*what does this print? */
printf(“\”The End.\” \n”);
printf(“\nA\nB\tC\nDE\aF\n”);
In addition to character constants and decimal values stored in chars, certain special characters can be produced via escape sequences.
ASCII value could be used
\a or char bell = 7;
\n or char newl = 10;
\f or char form = 12;

46. 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);

47. 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

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. scanf() int customer_status = 2; 2 ? Scanf() can
scanf(“%d”, &customer_status);
before scanf()
after scanf()
address operator
only conversion code(s)
no plain text
customer_status ?
Scanf() can
input all types of data
input only specific characters
Skip or exclude specific characters
new value is whatever
was keyed by user

50. Conversion Specifiers for Input Statements
Frequently Used

51. Sample Code #include <stdio.h> main() { int customer_status = 2;
output would be as follows:
Starting with Status = 2
Enter new status: 5(value entered by user)
New status value is 5
#include <stdio.h>
main() {
int customer_status = 2;
printf(“Starting with Status = %d\n”, customer_status);
printf(“Enter new status: “); /* prompt user */
scanf(“%d”, &customer_status);
printf(“\nNew status value is %d\n”, customer_status); }
Identify parts of the program, variables, etc.
Note use of preprocessor statement; Use in all programs & we will discuss later
Point out printf() uses value of variable, while scanf() uses & to indicate address of variable, not value
Indicate still a very simple program with much missing

52. Data Stream with scanf()
main() {
char letter1, letter2, letter3;
int num1, num2;
float fpnum;
double dblnum;
scanf(“%c”, &letter1);
scanf(“%c”, &letter2);
scanf(“%c”, &letter3);
scanf(“%d”, &num1);
scanf(“%f”, &fpnum);
scanf(“%lf”, &dblnum);
printf(“int num is %d\n”, num1);
printf(“fpnum is %f”, fpnum);
printf(“letter1 is %c, value %d\n”, letter1, letter1); }
How would this program work
with the following input data?
(The box represents the input
data stream, or buffer)
represents
‘Enter’ key

53. Data Stream with scanf()
input data stream
Why is this needed?
scanf(“%c”, &letter1);
scanf(“%c”, &letter2);
scanf(“%c”, &letter3);
scanf(“%d”, &num1);
scanf(“%f”, &fpnum);
scanf(“%lf”, &dblnum);
printf(“int num is %d\n”, num1);
printf(“fpnum is %f\n”, fpnum);
printf(“letter1 is %c, value %d\n”, letter1, letter1);

54. 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

55. Syntax Errors You have broken the C "rules of grammar"
The compiler may report several errors for one mistake (That's C for you)
Fix the syntax errors one at a time and recompile
Don't despair!
Warnings ought to be fixed too.

56. Compiler Listing with Syntax Errors
1 /* Calculates and displays the area and circumference of a circle */
2 #include <stdio.h>
268 #define PI
269
270 int
271 main(void)
272 {
double area, circum
/* Get circle radius */
printf("Enter radius> ");
***** Semicolon added at the end of the previous source line

57. Compiler Listing with Syntax Errors
scanf("%lf", &radius);
***** Identifier "radius" is not declared within this scope
***** Invalid operand of address-of operator
278
/* Calculate the area */
area = PI * radius * radius;

58. Compiler Listing with Syntax Errors
281
/* Calculate the circumference */
circum = 2 * PI * radius;
***** Identifier "radius" is not declared within this scope
284
/* Display the area and circumference * /
printf("The area is %f\n", area);
printf("The circumference is %f\n", circum);
return (0);
289 }
***** Unexpected end-of-file encountered in a comment
***** "}" inserted before end-of-file

59. Link-Time Errors After compilation, there may be link errors
Inconsistent function names
No "main"
More than one "main"
The compiler being awkward (save and re-invoke the studio)

60. Run-Time (Semantic) Errors
The program does not do what you want
This is nearly always your own error
Look carefully through the code
Else use the debugger (we meet this later)

61. 111 #include <stdio.h>
262
263 int
264 main(void)
265 {
int first, second;
double temp, ans;
printf("Enter two integers> ");
scanf("%d%d", &first, &second);
temp = second + first;
ans = first / temp;
printf("The result is %.3f\n", ans);
273
return (0);
275 }
Enter two integers> -3 3
Arithmetic fault, divide by zero at line 272 of routine main

62. Undetected Errors
Incorrect results probably due to Character and Numeric scanning problem
Incorrect results probably due to & omission
Debugging a problem is very time-consuming
Plan your program carefully and check them to eliminate bugs before running the program

63. /* Incorrect revision of welcoming message program */
#include <stdio.h> /* printf, scanf definitions */
int
main(void) {
char letter_1, letter_2, letter_3; /* three letters */
int year; /* current year */
printf("Enter the current year and press return> ");
scanf("%d", &year);
printf("Enter a 3-letter nickname and press return> ");
scanf("%c%c%c", &letter_1, &letter_2, &letter_3);
printf("Welcome, %c%c%c. %d is a great year to study C!\n",
letter_1, letter_2, letter_3, year);
return (0); }
Enter the current year and press return> 1994
Enter a 3 letter nickname and press return> Bob
Welcome,
Bo is a great year to study C!

64. #include <stdio.h>
int
main(void) {
int first, second, sum;
printf("Enter two integers> ");
scanf("%d%d", first, second); /* ERROR!! should be &first, &second */
sum = first + second;
printf("%d + %d = %d\n", first, second, sum);
return (0); }
Enter two integers> 14 3 =

65. Library Functions

66. 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.

67. Exercise Evaluate the following: floor(15.8) floor(15.8+0.5)
ceil(-7.2) *pow(4.0,2.0)
sqrt(floor(fabs(-16.8)))
log10(1000.0)

68. 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 [-, ].

69. 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); */

70. 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));

71. 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);

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

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

74. 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

75. 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)

76. 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); }

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

78. 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.

79. 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); }