Programming

1
Programming

• Loops

2
Incremental Operators

• Used as a short-hand

i a ?? i i a i - a ?? i i -
a i a ?? i i a i / a ?? i i /
a i or i ?? i i 1 ?? i 1 i-- or
--i ?? i i 1 ?? i - 1
3
Loops

• Used to repeat the same code segmaent over and
  over again.

Block of code Some changing state
Loop while some condition holds
4
Loops

• C provides some flexible ways of deciding how
  many times to loop, or when to exit a loop.
• for, while, do-while loops.

5
while loops

• while (expression)
• statement

• The statement is executed as long as condition
  is true.
• The loop terminates when the condition is no
  longer true.

6
Example - Factorial

• int main()
• int i 0, n 0, fact 1
• printf("Enter a number\n")
• scanf("d", n)
• i 1 / this is the counter /
• while (i lt n)
• fact i
• i
• printf("the factorial is d\n", fact)
• return 0

7
Example Fibonacci series
0 1 1 2 3 5 8 13 21 34
0 1
0 1 1 2 3 5 8 13 21
0 1 1 2
0 1 1
0 1 1 2 3 5 8 13 21 34



8
Fibonacci step by step
lim
fib1
fib2
fib_next

• int fib1 0, fib2 1, fib_next 0,
  lim
• ...
• printf("d ", fib1)
• while (fib2 lt lim)
• printf("d ", fib2)
• fib_next fib1 fib2
• fib1 fib2
• fib2 fib_next
• printf("\n")

5
0
1
---
Screen
0
9
Fibonacci step by step
lim
fib1
fib2
fib_next

• int fib1 0, fib2 1, fib_next 0,
  lim
• ...
• printf("d ", fib1)
• while (fib1 lt lim)
• printf("d ", fib2)
• fib_next fib1 fib2
• fib1 fib2
• fib2 fib_next
• printf("\n")

5
0
1
---
Screen
0
10
Fibonacci step by step
lim
fib1
fib2
fib_next

• int fib1 0, fib2 1, fib_next 0,
  lim
• ...
• printf("d ", fib1)
• while (fib2 lt lim)
• printf("d ", fib2)
• fib_next fib1 fib2
• fib1 fib2
• fib2 fib_next
• printf("\n")

5
0
1
---
Screen
0 1
11
Fibonacci step by step
lim
fib1
fib2
fib_next

• int fib1 0, fib2 1, fib_next 0,
  lim
• ...
• printf("d ", fib1)
• while (fib2 lt lim)
• printf("d ", fib2)
• fib_next fib1 fib2
• fib1 fib2
• fib2 fib_next
• printf("\n")

5
0
1
1
Screen
0 1
12
Fibonacci step by step
lim
fib1
fib2
fib_next

• int fib1 0, fib2 1, fib_next 0,
  lim
• ...
• printf("d ", fib1)
• while (fib2 lt lim)
• printf("d ", fib2)
• fib_next fib1 fib2
• fib1 fib2
• fib2 fib_next
• printf("\n")

5
1
1
1
Screen
0 1
13
Fibonacci step by step
lim
fib1
fib2
fib_next

• int fib1 0, fib2 1, fib_next 0,
  lim
• ...
• printf("d ", fib1)
• while (fib2 lt lim)
• printf("d ", fib2)
• fib_next fib1 fib2
• fib1 fib2
• fib2 fib_next
• printf("\n")

5
1
1
1
Screen
0 1
14
Fibonacci step by step
lim
fib1
fib2
fib_next

• int fib1 0, fib2 1, fib_next 0,
  lim
• ...
• printf("d ", fib1)
• while (fib2 lt lim)
• printf("d ", fib2)
• fib_next fib1 fib2
• fib1 fib2
• fib2 fib_next
• printf("\n")

5
1
1
1
Screen
0 1
15
Fibonacci step by step
lim
fib1
fib2
fib_next

• int fib1 0, fib2 1, fib_next 0,
  lim
• ...
• printf("d ", fib1)
• while (fib2 lt lim)
• printf("d ", fib2)
• fib_next fib1 fib2
• fib1 fib2
• fib2 fib_next
• printf("\n")

5
1
1
1
Screen
0 1 1
16
Fibonacci step by step
lim
fib1
fib2
fib_next

• int fib1 0, fib2 1, fib_next 0,
  lim
• ...
• printf("d ", fib1)
• while (fib2 lt lim)
• printf("d ", fib2)
• fib_next fib1 fib2
• fib1 fib2
• fib2 fib_next
• printf("\n")

5
1
1
2
Screen
0 1 1
17
Fibonacci step by step
lim
fib1
fib2
fib_next

• int fib1 0, fib2 1, fib_next 0,
  lim
• ...
• printf("d ", fib1)
• while (fib2 lt lim)
• printf("d ", fib2)
• fib_next fib1 fib2
• fib1 fib2
• fib2 fib_next
• printf("\n")

5
1
1
2
Screen
0 1 1
18
Fibonacci step by step
lim
fib1
fib2
fib_next

• int fib1 0, fib2 1, fib_next 0,
  lim
• ...
• printf("d ", fib1)
• while (fib2 lt lim)
• printf("d ", fib2)
• fib_next fib1 fib2
• fib1 fib2
• fib2 fib_next
• printf("\n")

5
1
2
2
Screen
0 1 1
19
Fibonacci step by step
lim
fib1
fib2
fib_next

• int fib1 0, fib2 1, fib_next 0,
  lim
• ...
• printf("d ", fib1)
• while (fib2 lt lim)
• printf("d ", fib2)
• fib_next fib1 fib2
• fib1 fib2
• fib2 fib_next
• printf("\n")

5
1
2
2
Screen
0 1 1
20
Fibonacci step by step
lim
fib1
fib2
fib_next

• int fib1 0, fib2 1, fib_next 0,
  lim
• ...
• printf("d ", fib1)
• while (fib2 lt lim)
• printf("d ", fib2)
• fib_next fib1 fib2
• fib1 fib2
• fib2 fib_next
• printf("\n")

5
1
2
2
Screen
0 1 1 2
21
Fibonacci step by step
lim
fib1
fib2
fib_next

• int fib1 0, fib2 1, fib_next 0,
  lim
• ...
• printf("d ", fib1)
• while (fib2 lt lim)
• printf("d ", fib2)
• fib_next fib1 fib2
• fib1 fib2
• fib2 fib_next
• printf("\n")

5
1
2
3
Screen
0 1 1 2
22
Fibonacci step by step
lim
fib1
fib2
fib_next

• int fib1 0, fib2 1, fib_next 0,
  lim
• ...
• printf("d ", fib1)
• while (fib2 lt lim)
• printf("d ", fib2)
• fib_next fib1 fib2
• fib1 fib2
• fib2 fib_next
• printf("\n")

5
2
2
3
Screen
0 1 1 2
23
Fibonacci step by step
lim
fib1
fib2
fib_next

• int fib1 0, fib2 1, fib_next 0,
  lim
• ...
• printf("d ", fib1)
• while (fib2 lt lim)
• printf("d ", fib2)
• fib_next fib1 fib2
• fib1 fib2
• fib2 fib_next
• printf("\n")

5
2
3
3
Screen
0 1 1 2
24
Fibonacci step by step
lim
fib1
fib2
fib_next

• int fib1 0, fib2 1, fib_next 0,
  lim
• ...
• printf("d ", fib1)
• while (fib2 lt lim)
• printf("d ", fib2)
• fib_next fib1 fib2
• fib1 fib2
• fib2 fib_next
• printf("\n")

5
2
3
3
Screen
0 1 1 2
25
Fibonacci step by step
lim
fib1
fib2
fib_next

• int fib1 0, fib2 1, fib_next 0,
  lim
• ...
• printf("d ", fib1)
• while (fib2 lt lim)
• printf("d ", fib2)
• fib_next fib1 fib2
• fib1 fib2
• fib2 fib_next
• printf("\n")

5
2
3
3
Screen
0 1 1 2 3
26
Fibonacci step by step
lim
fib1
fib2
fib_next

• int fib1 0, fib2 1, fib_next 0,
  lim
• ...
• printf("d ", fib1)
• while (fib2 lt lim)
• printf("d ", fib2)
• fib_next fib1 fib2
• fib1 fib2
• fib2 fib_next
• printf("\n")

5
2
3
5
Screen
0 1 1 2 3
27
Fibonacci step by step
lim
fib1
fib2
fib_next

• int fib1 0, fib2 1, fib_next 0,
  lim
• ...
• printf("d ", fib1)
• while (fib2 lt lim)
• printf("d ", fib2)
• fib_next fib1 fib2
• fib1 fib2
• fib2 fib_next
• printf("\n")

5
3
3
5
Screen
0 1 1 2 3
28
Fibonacci step by step
lim
fib1
fib2
fib_next

• int fib1 0, fib2 1, fib_next 0,
  lim
• ...
• printf("d ", fib1)
• while (fib2 lt lim)
• printf("d ", fib2)
• fib_next fib1 fib2
• fib1 fib2
• fib2 fib_next
• printf("\n")

5
3
5
5
Screen
0 1 1 2 3
29
Fibonacci step by step
lim
fib1
fib2
fib_next

• int fib1 0, fib2 1, fib_next 0,
  lim
• ...
• printf("d ", fib1)
• while (fib2 lt lim)
• printf("d ", fib2)
• fib_next fib1 fib2
• fib1 fib2
• fib2 fib_next
• printf("\n")

5
3
5
5
Screen
0 1 1 2 3
30
Fibonacci step by step
lim
fib1
fib2
fib_next

• int fib1 0, fib2 1, fib_next 0,
  lim
• ...
• printf("d ", fib1)
• while (fib2 lt lim)
• printf("d ", fib2)
• fib_next fib1 fib2
• fib1 fib2
• fib2 fib_next
• printf("\n")

5
3
5
5
Screen
0 1 1 2 3
31
getchar

• getchar() gets a single character from the user.
• Requires including stdio.h
• Returns a non-positive number on failure.
• Similar to scanf.

char c c getchar()
char c scanf("c", c)
??
32
putchar

• putchar(char c) prints out the character inside
  the brackets.
• Requires including stdio.h
• Similar to printf.

char c putchar(c)
char c printf("c", c)
??
33
Example - Copy

• int main()
• int c
• c getchar()
• while (c ! '\n')
• putchar(c)
• c getchar()
• return 0

34
Exercise Low to Up

• Read input from the user until end-of-line (\n)
  encountered.
• Convert lowercase letters to uppercase ones.

35
Solution Low to Up

• int main()
• int c 0
• printf ("Please enter a string ")
• c getchar()
• while (c ! '\n')
• if (c gt 'a' c lt 'z')
• putchar(c - 'a' 'A')
• else
• putchar(c)
• c getchar()
• putchar('\n')
• return 0

36
break in a loop

• When break is encountered, the loop is stopped
  regardless of whether the condition is still
  true.
• The program then continues to run from the first
  line after the while loop.
• If called within a nested loop, break breaks out
  of the inner loop only.

37
Example what does this do?

• int main()
• int i 0, c
• printf("Enter a line of text\n")
• c getchar()
• while (c ! '\n')
• if (c ' ')
• break
• i
• c getchar()

38
Example Counting Letters

• int main()
• int counter 0, c
• printf("Enter a line of text\n")
• c getchar()
• while (c ! '\n')
• if (c ' ') / found the first space - exit
  the loop /
• break
• counter
• c getchar()
• if (c ' ') / we found a space /
• printf("There are d letters before the
  first space.\n", counter)
• else / The loop ended without
  finding spaces /
• printf("There are no spaces in the input
  line.\n")
• return 0

39
continue

• When continue is encountered, the rest of the
  loop body is ignored.
• The program then continues to run from the
  beginning of the loop.

40
What does it do?

• int main()
• int i
• i 1
• while (i lt 10)
• if (i 2 0)
• break
• printf("d\n", i)
• i
• printf("The End\n")
• return 0

1The End
41
and this?

• int main()
• int i
• i 1
• while (i lt 10)
• if (i 2 0)
• continue
• printf("d\n", i)
• i
• printf("The End\n")
• return 0

Infinite Loop!
42
for loops

• for (ltinitializationgt ltconditiongt ltincrementgt)
      statement(s)

43
Example - Factorial Using for
i
n
fact

• int main()
• int i, n, fact 1
• printf("Enter a number\n")
• scanf("d", n)
• for (i 1 i lt n i)
• fact i
• printf("the factorial is d\n", fact)
• return 0

---
---
1
44
Example - Factorial Using for
i
n
fact

• int main()
• int i, n, fact 1
• printf("Enter a number\n")
• scanf("d", n)
• for (i 1 i lt n i)
• fact i
• printf("the factorial is d\n", fact)
• return 0

---
3
1
45
Example - Factorial Using for
i
n
fact

• int main()
• int i, n, fact 1
• printf("Enter a number\n")
• scanf("d", n)
• for (i 1 i lt n i)
• fact i
• printf("the factorial is d\n", fact)
• return 0

1
---
3
1
46
Example - Factorial Using for
i
n
fact

• int main()
• int i, n, fact 1
• printf("Enter a number\n")
• scanf("d", n)
• for (i 1 i lt n i)
• fact i
• printf("the factorial is d\n", fact)
• return 0

1
3
1
47
Example - Factorial Using for
i
n
fact

• int main()
• int i, n, fact 1
• printf("Enter a number\n")
• scanf("d", n)
• for (i 1 i lt n i)
• fact i
• printf("the factorial is d\n", fact)
• return 0

2
3
1
48
Example - Factorial Using for
i
n
fact

• int main()
• int i, n, fact 1
• printf("Enter a number\n")
• scanf("d", n)
• for (i 1 i lt n i)
• fact i
• printf("the factorial is d\n", fact)
• return 0

2
---
3
1
49
Example - Factorial Using for
i
n
fact

• int main()
• int i, n, fact 1
• printf("Enter a number\n")
• scanf("d", n)
• for (i 1 i lt n i)
• fact i
• printf("the factorial is d\n", fact)
• return 0

2
3
2
50
Example - Factorial Using for
i
n
fact

• int main()
• int i, n, fact 1
• printf("Enter a number\n")
• scanf("d", n)
• for (i 1 i lt n i)
• fact i
• printf("the factorial is d\n", fact)
• return 0

3
3
2
51
Example - Factorial Using for
i
n
fact

• int main()
• int i, n, fact 1
• printf("Enter a number\n")
• scanf("d", n)
• for (i 1 i lt n i)
• fact i
• printf("the factorial is d\n", fact)
• return 0

3
3
6
52
Example - Factorial Using for
i
n
fact

• int main()
• int i, n, fact 1
• printf("Enter a number\n")
• scanf("d", n)
• for (i 1 i lt n i)
• fact i
• printf("the factorial is d\n", fact)
• return 0

4
3
6
53
Example - Factorial Using for
i
n
fact

• int main()
• int i, n, fact 1
• printf("Enter a number\n")
• scanf("d", n)
• for (i 1 i lt n i)
• fact i
• printf("the factorial is d\n", fact)
• return 0

4
---
3
6
54
Example - Factorial Using for
i
n
fact

• int main()
• int i, n, fact 1
• printf("Enter a number\n")
• scanf("d", n)
• for (i 1 i lt n i)
• fact i
• printf("the factorial is d\n", fact)
• return 0

4
---
3
6
55
What does it do?

• int main()
• int i
• for (i 1 i lt 10 i)
• if (i 2 0)
• break
• printf("d\n", i)
• printf("The End\n")
• return 0

1The End
56
and this?

• int main()
• int i
• for (i 1 i lt 10 i)
• if (i 2 0)
• continue
• printf("d\n", i)
• printf("The End\n")
• return 0

13579The End
57
Nested Loops

• Loops can be nested
• For every time in the external loop we make a
  complete iteration of the internal one.

58
Example - Multiplication Table

• int main()
• int row, col
• for (row 1 row lt 10 row)
• for (col 1 col lt 10 col)
• printf("3d", row col)
• printf("\n")
• return 0

59
Output

• 1 2 3 4 5 6 7 8 9 10
• 2 4 6 8 10 12 14 16 18 20
• 3 6 9 12 15 18 21 24 27 30
• 4 8 12 16 20 24 28 32 36 40
• 5 10 15 20 25 30 35 40 45 50
• 6 12 18 24 30 36 42 48 54 60
• 7 14 21 28 35 42 49 56 63 70
• 8 16 24 32 40 48 56 64 72 80
• 9 18 27 36 45 54 63 72 81 90
• 10 20 30 40 50 60 70 80 90 100

60
Example Reverse Triangle

• int main()
• int i 0, j 0
• int size 0
• printf("Please enter a size\n")
• scanf("d", size)
• for (i 0 i lt size i)
• for (j i j lt size j)
• printf("")
• printf("\n")
• return 0

Please enter a size 5
61
Exercise Prime Numbers

• Write a program that prints all the prime numbers
  smaller than or equal to N.
• N is given by the user (input)
• How do you go over all the numbers lt N?
• How do you know if a number is prime?

62
Solution Prime Numbers

• int main()
• int candidate 0, divisor 0, last 0
• printf("Enter a number\n")
• scanf("d", last)
• for (candidate 2 candidate lt last
  candidate)
• for (divisor 2 divisor lt candidate
  divisor)
• if (candidate divisor 0)
• break
• if (divisor candidate)
• printf("the number d is prime\n",
  candidate)
• return 0

63
do-while loops
Statement

• do
• statement(s)
• while (condition)
• Similar to while loops
• Except the condition is evaluated after the loop
  body
• The loop body is always executed at least once,
  even if the expression is never true

condition
true
false
64
Example Waiting for Legal Input

• int main()
• int i 0
• printf("Please enter a positive number.\n")
• do
• scanf("d", i)
• if (i lt 0)
• printf("Try again.\n")
• while (i lt 0)
• / The program continues.... /
• return 0