Programming and Data Structure

1
Programming and Data Structure

• Sudeshna Sarkar

Lecture 7
2

• main ()
• int sum0
• int input, inner, outer
• printf(Input an integer )
• scanf (d, input)
• for (outer1 outer lt input outer)
• for (inner0 inner lt outer inner)
• sum inner
• printf (The result is d\n, sum)

3
Some Loop Pitfalls

• while (sum lt NUM)
• sum sum2

for (i0 iltNUM i) sum sumi
for (i1 i!10 ii2) sum sumi
double x for (x0.0 xlt10.0 xx0.2)
printf(.18f, x)
4
Doubles and floats

• What you expect
• 0.000000000000000000
• 0.200000000000000000
• 0.400000000000000000
• .. .. ..
• 9.000000000000000000
• 9.200000000000000000
• 9.400000000000000000
• 9.600000000000000000
• 9.800000000000000000

What you may get 0.000000000000000000 0.200000000
000000000 0.400000000000000000 .. ..
.. 8.999999999999999999 9.199999999999999999 9.399
999999999999999 9.59999999999999999 9.799999999999
999999
5
Use ints as loop counters

• int i
• double x
• for (i0 ilt50 ii1)
• x (double)i/5.0
• printf (.18f, x)

6
Iteration Summary

• General Pattern
• initialize
• test
• do stuff
• update
• go back to re-test, re-do stuff, re-update, ...
• while and for are equally general in C
• use for when initialize/test/update are simple,
  especially when counting.

7
Event Driven Programming

• General Pattern
• Program starts, sets itself up.
• Waits for some event or command to happen
• mouse click, key click, timer, menu selection
  etc.
• Program performs operation (handles the
  command)
• Program goes back to waiting.

8
Simple Command Interpreter

• Read in commands and execute them.
• Input - single characters
• a - execute command Add by calling Add()
• s - execute command Sub by calling Sub()
• q - quit
• Pseudocode for main loop
• get next command
• if a, execute command Add()
• if b, execute command Sub()
• if q, signal quit

9
Command Interpreter Loop Control

• repeat until quit signal
• use variable done to indicate when done

set done to false while not done body
statements if quit command, set done to
true
10
Command Interpreter program
switch (command) case A
case a Add()
break case S case s
Sub() break
case Q case q doneTRUE

• define FALSE 0
• define TRUE 1
• int main (void)
• char command
• int done FALSE
• while (!done)
• printf (Input command)
• scanf(c,command)

11
Exercise a

• Write a C program which accepts as input a single
  integer k, then writes a pattern consisting of a
  single 1 on the first line, two 2s on the 2nd
  line, three 3s on the 3rd line, until it writes k
  occurrences of k on the last line.
• For example, if the input is 4, the output should
  be
• 1
• 2 2
• 3 3 3
• 4 4 4 4

12
Exercise b

• Write a C program which accepts as input a single
  integer k, then generates the following pattern
  of k lines
• For example, if the input is 5, the output should
  be
• 1
• 2 2 2
• 3 3 3 3 3
• 4 4 4 4 4 4 4
• 5 5 5 5 5 5 5 5 5

13
Test if a number is prime

• prime 1
• for (i2 iltnum i)
• if (numi 0)
• prime0
• if (prime 1)
• printf (d is a prime number\n)

14
Test if a number is prime

• prime 1
• limit sqrt ((double)num)
• for (i2 iltlimit i)
• if (numi 0)
• prime0
• break
• if (prime 1)
• printf (d is a prime number\n)

15
Break and continue

• These two statements are used in loop control
• break exits the innermost current loop (for,
  while, do-while) and to exit from a switch
• Control will be transferred out of the loop
• continue starts the next iteration of the loop
  (for, while, do-while)
• used to bypass the remainder of the current pass
  through a loop

16

• do
• scanf (f, x)
• if (xlt0)
• printf(Error, neg x)
• break
• . . .
• /process non-neg x /
• while (xlt100)

for (count0countltncount) . . .
while ((cgetchar()) ! \n)
if (c) break . . .

17

• do
• scanf (f, x)
• if (xlt0)
• printf(Neg value forx)
• continue
• . . .
• /process non-neg x /
• while (xlt100)

18
Ex Write a loop that will calculate the sum of
an AP series upto n terms

• Sum a (ad) (a2d) . . . (a (n-1)d)

sum a for (i1 iltn i) sum sum
a id printf (d, sum)
sum a term a for (i1 iltn i)
term term d sum sum
term printf (d, sum)
19
Exercise c

• Write a C program that takes as input a positive
  integer n, and prints all prime numbers between 2
  and n.

20
Exercise d

• Write a C program that calculates the sum of the
  first n odd numbers
• 1 3 5 . . . 2n-1

21
The sine of x can be calculated approximately by
summin the first n terms of the infinite series
sin x x - x3 /3! x5 /5! x7 /7! . . .

• where x is expressed in radians (p radians 180
  degrees).
• Write a C program that will read in a value for x
  and will calculate its sine.
• (i) sum the first n terms
• (ii)continue adding successive terms till the
  value of the next term becomes smaller (in
  magnitude) than 10-5

22
scanf (f, x) x xPI/180.0 sineval x
term x for (i1 iltn i) term
(-1)termxx/(2i(2i1)) sineval
sineval term
23
scanf (f, x) x xPI/180.0 sineval x
term x for (i1 termlt0.00001 i)
term (-1)termxx/(2i(2i1))
sineval sineval term printf (The value of
sine is f to d terms\n,sineval,
i)