Repeated Calculations

1
Repeated Calculations
Lect05

• To obtain the areas of several circles, we would
  have to run our program several times.
• There are many times when we will want to repeat
  calculations and C has looping structures built
  in
• while
• do while
• for

2
while - Statement

• while (condition) operations
• The operations in the while block are performed
  as long as (while) the condition is true.
• When the condition becomes false, the while loop
  completes and control moves to the instruction
  following the while loop.

3
while - An Example

• float area, pi3.14159, radius1.0
• while(radiusgt0.0)
• printf("Input radius ")
• scanf("f", radius)
• areapiradiusradius
• printf("Area is f\n", area)
• printf("End of program\n")

Lect0501.c
4
Notes

• The entry value of the while condition must be
  specified.
• radius1.0 is the entry condition.
• There must be a termination condition for the
  while loop.
• providing a value of radiuslt0.0 will stop the
  loop.

5
Repetition - while
TRUE
FALSE
6
Remember the if
TRUE
FALSE
7
Repetition - do while
TRUE
FALSE
8
do while - Statement

• To prevent having to deliberately set a value for
  the while condition on entry to the loop, the do
  while structure has been provided.
• In the do while, the condition is tested at the
  end of the block rather than at the beginning.

9
do while - Example

• float area, pi3.14159, radius
• do
• printf("Input radius ")
• scanf("f", radius)
• areapiradiusradius
• printf("Area is f\n", area)
• while(radiusgt0.0)
• printf("End of program\n")

Lect0502.c
10
while OR do while?

• while is used when the program naturally sets the
  while condition before entry to the loop.
• do while is used when the while condition is
  undefined outside of the loop.

11
Counting

• Some applications require a loop which performs
  in a sequential manner or counting.
• Consider the sum of the first ten integers
• 123...10

12
Sum of First Ten Integers

• int main()
• int i1, sum0
• while(ilt11)
• sumsumi
• i //equivalent to ii1
• printf("Sum is d\n", sum)
• system("PAUSE")
• return 0

Lect0503.c
13
Notes i

• Now we see that the next language after C i.e.
  C1 is called C.

14
Notes sumsumi

• sumsumi
• In mathematics this would mean that
  i0 (sum-sumi)
• All should now be clear about "" being is
  assigned the value of
• The variable sum is assigned the value of (the
  old value of the variable sum plus the value of
  the variable i)

15
for - Statement

• An alternative method uses the for loop
• for (start setting looping condition step)
  operations
• Note the separation of the three terms in the for
  header by

16
Repetition - for
Initial setting
TRUE
Looping condition
Step
Body
FALSE
17
Sum of First Ten Integers - 2

• include ltstdio.hgt
• int main()
• int i, sum0
• for(i1 ilt11 i) sumsumi
• printf("Sum is d\n", sum)
• system("PAUSE")
• return 0

Lect0504.c
18
Sum of Numbers
i1
Initial setting
TRUE
sumsumi
i
ilt11
Looping condition
Step
Body
FALSE
19
Compare while and for

• int i1, sum0
• while(ilt11)
• sumsumi
• i
• for(i1 ilt11 i) sumsumi

20
Nested Loops

• int i, n, sum
• do
• printf("Sum of how many numbers? ")
• scanf("d", n)
• sum0
• for(i1 iltn i) sumsumi
• printf("Sum is d\n", sum)
• while(ngt0)

Lect0505.c
21
Nested Loops - 2

• int i, n, sum
• for(n1 nlt11 n)
• sum0
• for(i1 iltn i) sumsumi
• printf("Sum of first d numbers is d\n", n,
  sum)

Lect0506.c
22
Console Output

• Sum of first 1 numbers is 1
• Sum of first 2 numbers is 3
• Sum of first 3 numbers is 6
• Sum of first 4 numbers is 10
• Sum of first 5 numbers is 15
• Sum of first 6 numbers is 21
• Sum of first 7 numbers is 28
• Sum of first 8 numbers is 36
• Sum of first 9 numbers is 45
• Sum of first 10 numbers is 55

23
3D Surface

• float x, y, z
• for(x-20.0 xlt25.0 xx2.0)
• for(y-12.0 ylt13.0 yy1.0)
• zxx(y10)(y10)
• printf("f,f,f\n", x, y, z)

Lect0507.c
24
Plot