Program looping

1
Program looping

• Why we need loop
• Make code concise for repetitive processes
• When to use loop
• Run a block of code repetitively
• Process multiple data using same procedure
• How to use loop
• for
• while
• do

2
for loop

• Format
• for( init_expression loop_condition
  loop_expression )
• program statement
• Flow

3
while loop

• Format
• while (loop_condition) program
  statement
• Flow

4
for loop vs while loop
for loop
while loop
5
Convert for loop to while loop

• while (loop_condition) program
  statement
• for( init_expression loop_condition
  loop_expression )
• program statement

init_expression while(loop_condition)
program statement loop_expression
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Convert for to while Example
init_expression while(loop_condition) program
statement loop_expression

• F 1
• N 10
• for(M1 MltN MM 1)
• F F M

F 1 N 10 M 1 while(MltN)
F F M M M 1
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do-while loop

• Format
• do      program statement while
  (loop_condition)

8
while and do-while loop
do      program statement while
(loop_condition)
while (loop_condition) program statement

• In while loop, program statement may never be
  evaluated. While in do-while loop, it is
  evaluated at least once

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Example
p 7
p 7
10
Example
p 1
p 6
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break

• Used to break out of a loop immediately
• Possibly due to detection of an error

int i for(i0 i lt 3 i)
printf(here\n) break
printf(there\n)
here
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continue

• Used to continue at the next point
• Possibly due to detection of an error

int i 0 for(i0 i lt 3 i)
printf(here\n) continue
printf(there\n)
here here here
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Example summation of valid scores

• count 0 n 10 sum 0
• while (count lt n)
• scanf("d", score)
• if (score lt 0 score gt 100)
• continue
• count
• sum sum score

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Example summation of valid scores

• count 0 n 10 sum 0
• while (count lt n)
• scanf("d", score)
• if (score lt 0 score gt 100)
• printf(Wrong data. Exiting program\n)
• break
• count
• sum sum score