Understanding Loops, Lists, Printing & Controls in VBA, Slides of C programming

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Loops, Lists, Printing

10_loops.ppt

Overview of Topics

• While Loop
• Do While Loop
• For Loop
• Pretest vs Posttest
• Nested Loops
• List and Combo Boxes
• Printing Controls

Flowchart Symbols

Begin or End Input or Output

Processing Decision

Branch or Direction of Flow

Flow Control Structures

• The order in which statements are

executed.

• There are four structures.
  1. Sequence Control Structure
  2. Selection Control Structure
     • Also referred to as branching (if and if-else)
  3. Case Control Structure (select)
  4. Repetition Control Structure (loops)

While is a Pretest Loop - Example

intCount = 1; //initialize controlling variable

while (intCount < 4)

{ txtCount.Text = intCount.ToString(“N0”); intCount++; //add one

}

Output:

1 2 3

While is a Pretest Loop

• Pretest - controlling condition is evaluated before executing loop body.
• Controlling variable must be initialized.
• Condition must be true to enter loop body.
• There is NO semi-colon after the condition.
• It is possible that body is not executed at all.
• Condition must be false to get out of loop.
• Controlling variable should be modified within the loop.
• Execution continues with next statement after Loop.

Do-While is a Posttest Loop -Example

intCount = 1; //initialize controlling variable

do

{ txtCount.Text = intCount.ToString(“N0”); intCount++;

} w hile (intCount < 4 );

Output:

1 2 3

Do-While Posttest Loop

• Posttest - controlling condition is evaluated after executing loop body.
• So, body is always executed at least one time.
• Initialization of controlling variable not necessarily required.
• Condition must be false to get out of loop.
• There is a semi-colon after the condition.
• Controlling variable should be modified within the loop.
• Execution continues with next statement after Loop.

Pretest vs. Posttest

• Pretest
  • For pretest loops the terminating condition is at the top of the loop.
  • It is possible that the body is not executed if the condition to get into the loop is not met.
• Posttest
  • For posttest loops the terminating condition is at the bottom of the loop.
  • The body is always executed at least one time.

Loop Summary

• Infinite loop
  • A loop that never ends.
  • While – condition always evaluates to true.
  • Controlling variable must be altered within the loop.
  • Click on the close form icon to stop the program.
  • Use Control-Break to enter debug mode.
• When to use a While or Do-While will become evident as we continue to use and learn each loop.
• Nested Loop is a loop inside another loop (see next slide).

For Loop

• Good when a task needs to be completed a

fixed number of times.

• Good when counting with fixed increments.
• Compares to a While Pretest loop.

for (initialization; condition; action)

body

For Loop

//For includes initialization and ending condition

for ( int intCount = 1; intCount < 4; intCount++;) { txtCount.Text = intCount.ToString(“N0”); }

Output:

1 2 3

Flowchart – For Pretest Loop

count = 1

while count < 4

Output count

count +

Next statement

False

True

Represents Skip or Exit Loop Loop

Nested For-Next Loops

• For loops may contain other For loops.
• The second loop must be completely

contained inside the first loop.

• The second loop should have a different

controlling variable.

• Should indent inner loops for readability.