C programming for Engineers

1
C programming for Engineers

• Lcc compiler a free C compiler available on the
  web.
• http//www.cs.virginia.edu/lcc-win32/
• Also available visual Studio C,
• Express edition
• http//msdn.microsoft.com/vstudio/express/visualc/
  download/
• Note that you have to register (free)

2
What are variables?

• A named area in the computer memory, intended to
  contain values of a certain kind (integers, real
  numbers, etc.)
• They contain the data your program works with.
• They can be used to store data to be used
  elsewhere in the program.
• In short they are the only way to manipulate
  data.

3
Variables in memory

• int my_int 5
• double my_double 3.5

5
my_int
3.5
my_double
4
Variables in memory

• Whenever we write the variable name (my_int), we
  ask to read the value of that variable
• If we write variable_name, we ask for the
  address of that variable

5
my_int
3.5
my_double
5
Example

• / Get a length in cm and convert to inches /
• include ltstdio.hgt
• int main()
• double cm, inches
• printf("Please enter length in centimeters ")
• scanf("lf", cm)
• inches cm / 2.54
• printf("This is equal to g inches\n", inches)
• return 0

6
Declaring variables in C
double cm, inches

• Before using a variable, one must declare it.
• The declaration first introduces the variable
  type, then its name.
• When a variable is declared, its value is
  undefined.

7
Example variable declarations

• int i
• char c
• float f1, f2
• float f17.0, f2 5.2
• unsigned int ui 0

8
Variable naming rules

• Letters, digits, underscores
• i
• CSE_5a
• a_very_long_name_that_isnt_very_useful
• fahrenheit
• First character cannot be a digit
• 5a_CSE is not valid!
• Case sensitive
• CSE_5a is different from cse_5a

9
Data types in C

• char a single byte character.
• int an integer number usually 4 bytes.
• float a single precision real number usually
  4 bytes.
• double a double precision real number usually
  8 bytes.

char
float
int
double
10
Data types in C

• short int (or just short) an integer number,
  usually 2 bytes (rarely used).
• long int (or just long) an integer number, 4
  or 8 bytes (rarely used).
• long double - a double precision real number
  usually 8 bytes (rarely used).
• unsigned vs. signed

11
That example again

• / Get a length in cm and convert to inches /
• include ltstdio.hgt
• int main()
• double cm, inches
• printf("Please enter length in centimeters ")
• scanf("lf", cm)
• inches cm / 2.54
• printf("This is equal to g inches\n", inches)
• return 0

12
printf and scanf

• printf prints to the screen.
• Can also accept variables and print their values.
• scanf gets values from the standard input and
  assigns them to variables.

13
printf can print variable values

• printf("zd\n", z)
• The sequence d is a special sequence and is not
  printed!
• It indicates to printf to print the value of an
  integer variable written after the printed string.

14
scanf gets input from the user

• scanf("lf", cm)
• This statement waits for the user to type in a
  double value, and stores it in the variable named
  cm.
• To get 2 doubles from the user, use
  scanf("lflf", var1, var2)

15
prinft/scanf conversion codes

• A ltconversion codegt in the printf/scanf string
  is replaced by the respective variable.
• c a character
• d an integer, u an unsigned integer.
• f a float
• lf a double
• g a nicer way to show a double (in printf)
• - the character (in printf)

16
One last time

• / Get a length in cm and convert to inches /
• include ltstdio.hgt
• int main()
• double cm, inches
• printf("Please enter length in centimeters ")
• scanf("lf",cm)
• inches cm / 2.54
• printf("This is equal to g inches\n", inches)
• return 0

17
Exercise

• Write a program that accepts as input -
• The Dollar-Shekel exchange rate
• An integer amount of dollars
• and outputs -
• The equivalent amount in Shekels

18
Solution

• include ltstdio.hgt
• int main()
• double shekels, xchange
• int dollars
• printf("Enter the US-NIS exchange rate ")
• scanf("lf", xchange)
• printf("Enter the amount of dollars ")
• scanf("d", dollars)
• shekels dollars xchange
• printf("d dollars g shekels\n", dollars,
  shekels)
• return 0

19
The int type

• The most common and efficient integer type.
• Ranges from -2,147,483,648 to 2,147,483,647.
• When you need to save memory and you are sure to
  use small numbers, use char or short.
• When you need very big numbers, use long.
• Otherwise, better use int.

20
The double type

• The most efficient floating point type.
• Range is
  2.2250710-308 1.7976910308
• When you need to save memory/time, use float
  (whose range is 1.1754910-38
  3.402821038)
• Otherwise, better use double.

21
Char is also a number!

• A char variable is used to store a text
  character
• Letters.
• Digits.
• Keyboard signs.
• Non-printable characters.
• But also small numbers (0 to 255 or -128 to 127).

22
Text as numbers

• Every character is assigned a numeric code.
• There are different sets of codes
• ASCII (American Standard Code for Information
  Interchange) most common.
• EBCDIC ancient, hardly used today.
• Maybe others.
• We will use ASCII.
• The ASCII table.

23
The ASCII Table
24
More about character encoding

• Most of the time, you don't care what the
  particular numbers are.
• The table above shows only 128 characters (7
  bits). Some are non-printable.
• Extended ASCII code contains 256 characters.

25
More about character encoding

• ASCII code 0 (NULL character) is important we
  will see it again.
• Note contiguous sets of numbers, upper case and
  lower case characters.

26
Example of char as both a character and a small
number

• include ltstdio.hgt
• int main()
• char i 'b'
• printf("i as a character is c\n", i)
• printf("i as an integer is d\n", i)
• printf("The character after c is c\n",
  i, i 1)
• return 0

27
Another example

• / Get the position of a letter in the abc /
• include ltstdio.hgt
• int main()
• char letter
• printf("Please enter a lowercase letter\n")
• scanf("c", letter)
• printf("The position of this letter in the abc
  is d\n", letter - 'a' 1)
• return 0

28
Exercise

• Write a program that accepts as input
• A lowercase letter
• and outputs
• The same letter in uppercase
• (e.g., if the input is g, the output should be
  G)

29
Solution

• / Convert a letter to uppercase /
• include ltstdio.hgt
• int main()
• char letter
• printf("Please enter a lowercase letter\n")
• scanf("c", letter)
• printf("This letter in uppercase is c\n",
  letter - 'a' 'A')
• return 0

30
Arithmetic operators

• An operator is an action performed on something
  (e.g. constants, variables).
• That something is called an operand.
• Common operators
• Assignment
• Addition
• Subtraction -
• Multiplication
• Division /
• Modulo

31
Example

• Arithmetic operators on variables - digits.c

32
Lets see how it works
num
sum

• int main()
• int sum, num
• sum 0
• printf("Enter 3-digits number\n")
• scanf("d", num)
• /extract the first digit/
• sum sum num 10
• num num / 10

1350
5198
Arbitrary numbers (garbage)
33
Lets see how it works
num
sum

• int main()
• int sum, num
• sum 0
• printf("Enter 3-digits number\n")
• scanf("d", num)
• /extract the first digit/
• sum sum num 10
• num num / 10

1350
5198
34
Lets see how it works
num
sum

• int main()
• int sum, num
• sum 0
• printf("Enter 3-digits number\n")
• scanf("d", num)
• /extract the first digit/
• sum sum num 10
• num num / 10

1350
0
35
Lets see how it works
num
sum

• int main()
• int sum, num
• sum 0
• printf("Enter 3-digits number\n")
• scanf("d", num)
• /extract the first digit/
• sum sum num 10
• num num / 10

1350
0
36
Lets see how it works
num
sum

• int main()
• int sum, num
• sum 0
• printf("Enter 3-digits number\n")
• scanf("d", num)
• /extract the first digit/
• sum sum num 10
• num num / 10

369
0
37
Lets see how it works
num
sum

• int main()
• int sum, num
• sum 0
• printf("Enter 3-digits number\n")
• scanf("d", num)
• /extract the first digit/
• sum sum num 10
• num num / 10

369
0
38
Lets see how it works
num
sum

• int main()
• int sum, num
• sum 0
• printf("Enter 3-digits number\n")
• scanf("d", num)
• /extract the first digit/
• sum sum num 10
• num num / 10

369
9
39
Lets see how it works
num
sum

• int main()
• int sum, num
• sum 0
• printf("Enter 3-digits number\n")
• scanf("d", num)
• /extract the first digit/
• sum sum num 10
• num num / 10

369
9
40
Lets see how it works
num
sum

• int main()
• int sum, num
• sum 0
• printf("Enter 3-digits number\n")
• scanf("d", num)
• /extract the first digit/
• sum sum num 10
• num num / 10

36
9
41
Lets see how it works

• /extract the second digit/
• sum sum num 10
• num num / 10
• /extract the third digit/
• sum sum num 10
• printf("The digits sum is d\n", sum)
• return 0

num
sum
36
9
42
Lets see how it works

• /extract the second digit/
• sum sum num 10
• num num / 10
• /extract the third digit/
• sum sum num 10
• printf("The digits sum is d\n", sum)
• return 0

num
sum
36
15
43
Lets see how it works

• /extract the second digit/
• sum sum num 10
• num num / 10
• /extract the third digit/
• sum sum num 10
• printf("The digits sum is d\n", sum)
• return 0

num
sum
36
15
44
Lets see how it works

• /extract the second digit/
• sum sum num 10
• num num / 10
• /extract the third digit/
• sum sum num 10
• printf("The digits sum is d\n", sum)
• return 0

num
sum
3
15
45
Lets see how it works

• /extract the second digit/
• sum sum num 10
• num num / 10
• /extract the third digit/
• sum sum num 10
• printf("The digits sum is d\n", sum)
• return 0

num
sum
3
15
46
Lets see how it works

• /extract the second digit/
• sum sum num 10
• num num / 10
• /extract the third digit/
• sum sum num 10
• printf("The digits sum is d\n", sum)
• return 0

num
sum
3
18
47
Operations with different types

• When operands of two different types are involved
  in an operation, the operand of the weaker type
  is promoted to the other type (int ? float ?
  double).
• The result of the operation is of the higher
  type.
• When the operands are of the same type, the
  result is of that type as well.

48
Operations with different types

• For example -
• 3 4 7
• 3.0 4 7.0
• 3 / 4 0 !!!
• 3.0 / 4 0.75

49
Operations with different types

• Sometimes it is desirable for a variable of one
  type to be considered as belonging to another in
  an operation
• We say the variable is cast to the new type.
• The casting operator is of the form (type)
• For example, (float)i casts the variable i to a
  float.

50
Casting variables

• include ltstdio.hgt
• int main()
• int a1, b2
• printf("d / d d\n", a, b, a/b)
• printf("d / d g\n", a, b, (float)a / b)

51
Example find whats wrong

• include ltstdio.hgt
• int main()
• int a 10
• int b 20
• printf("The average of d and d is d\n",
  a, b, (a b) (1 / 2))
• return 0

52
Will this work?

• include ltstdio.hgt
• int main()
• int a 10
• int b 20
• printf ("The average of d and d is d\n",
  a, b, (a b)(1.0 / 2))
• return 0

53
The unsigned qualifier

• Normally, the last bit of a variable serves as a
  sign bit.
• In unsigned variables, it has the same role as an
  ordinary bit.
• Because of the extra bit, the range of possible
  values is doubled but only for positive
  numbers.
• For example, unsigned chars can range from 0 to
  255 while (signed) chars range from -128 to 127.
• To declare a variable as unsigned, add the
  unsigned keyword before its type. For example
• unsigned int ui

54
Overflow

• Happens when a variable gets assigned a value
  that is outside of its range
• This is equivalent to saying that the number of
  bits required to encode the value exceeds the
  number of bits in the variable
• The value of the variable will usually be
  non-sense

55
Overflow An example

• include ltstdio.hgt
• int main()
• int iA 1000
• int iB 1000000
• int iC 3000000
• int iD 5000000
• printf ("d d d\n", iA, iB, iAiB)
• printf ("d d d\n", iA, iC, iAiC)
• printf ("d d d\n", iA, iD, iAiD)
• return 0

56
Thank you

• See you next time!