VISUAL C++ PROGRAMMING: CONCEPTS AND PROJECTS Chapter 5A Repetition (Concepts)

Objectives Visual C++ Programming 2  Learn the strengths and weaknesses of user- controlled repetition  Study the various forms of repetition control structures  Learn how pre- and post-test loops work  Use for loops, while loops, and do...while loops

Objectives (continued) Visual C++ Programming 3  Generate random numbers  Learn how the loop process relates to summation, counting, and other common tasks  Use a loop to construct an extended string of characters

User-Controlled Repetition Visual C++ Programming 4  User-controlled repetition relies on the user to perform repeated actions  Entering data into textboxes  Clicking buttons  The need for user-controlled repetition  Consider a program that requires the user to enter 5 numbers into 5 textboxes  This program is difficult to revise to accommodate more or fewer numbers  Example: revising it to accommodate 15

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User-Controlled Repetition (continued) Visual C++ Programming 10  The problem with the previous examples were that they were designed to solve only one version of a broader problem  Single-purpose solution Works only with one set of input values  General purpose solution Works with any amount of input values  General averaging program  Uses user-controlled repetition  Handles any amount of input  Very few variables and interface controls  No need to change it to accommodate more data

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Accumulating a Sum and Counting Visual C++ Programming 15  Summation is the process of adding values to arrive at a sum  Accumulating a sum  A sum can be accumulated one addition at a time in a repetitive process  Counting  A process in which the value 1 is added to a counter in a repetitive process

Instance Variables Visual C++ Programming 16  Variable scope  Local scope The variable is declared in an event handler The variable exists only within that event handler  Class scope The variable is declared within the Form1 class but outside of all event handlers Every event handler can use it Called instance variables  Instance variables are declared  Immediately after the line #pragma endregion  Outside of all event handlers

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Instance Variables (continued) Visual C++ Programming 18  Instance variables are required for summation or counting  They are initialized to 0 by default when declared  Example: sum, count  Each time the user clicks the button a value is added to the sum and 1 is added to the count

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Repetition Control Structures Visual C++ Programming 20  Repetition control structures allow your program to automatically repeat one or more statements (not user- controlled)  Commonly called loops  Loop body - the statements in a loop  Iteration – a pass through the loop body  Loop condition – Boolean expression that must be true for further iteration to continue  Loop control variable – a variable used in the loop condition  Types of loops  Pre-test loop – loop condition comes before loop body  Post-test loop – loop condition comes after the loop body

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The while Loop Visual C++ Programming 22  A pre-test loop  Keyword while, followed by a loop condition and then the loop body  Repetition of the loop body continues as long as the pre-test evaluates to true  Repetition stops when the pre-test evaluates to false. Control transfers to the next statement after the loop

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The while Loop (continued) Visual C++ Programming 26  Incrementation  Adding 1 to a loop control variable  Shorthand version: num += 1;  Prefix incrementation: ++num;  Postfix incrementation: num++;  Decrementation  Subtracting 1 from a loop control variable  Shorthand version: num -= 1;  Prefix decrementation: --num;  Postfix decrementation: num--;

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do…while Loops Visual C++ Programming 29  Post-test loop condition  Keyword do at top of loop, followed by loop body, then keyword while followed by the loop condition  Repetition of the loop body continues as long as the post-test evaluates to true  Repetition stops and control is transferred to the first statement after the loop when the post-test evaluates to false

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The for Loop Visual C++ Programming 33  Pre-test loop  Built-in loop control variable that often serves as a counter  Three clauses in the for statement  Initialization of loop control variable  Pre-test condition  Update of loop control variable  The initialization clause is executed only once, when the loop is first encountered  The update clause is executed at the end of each iteration, prior to the pre-test evaluation

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Common Loop Tasks Visual C++ Programming 44  Formula translation  Accumulating a product  Building a string  Generating random numbers  Finding the largest/smallest value  Counting specific values  Nested loops

Formula Translation Visual C++ Programming 45  Summation  Initial value  Terminal value  Summation process  Can easily be translated from mathematical symbols into C++ code

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Accumulating a Product Visual C++ Programming 49  Like summation only with multiplication  Factorial 0! = 1, 1! = 1, n! = n x (n-1)! 5! Is 5 x 4 x 3 x 2 x 1  Initialize the product to 1 outside of the loop  The loop multiplies the product by succesive values

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Building a String Visual C++ Programming 52  Repeat the process of adding a new character to a String variable within the loop body  Declare an empty string outside the loop  Add a new character to it with each iteration  Concatenating characters  Uses the concatenation operator +  Or the shorthand concatenation operator +=  Conversion to String type is implicit ( ToString() is not required)

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Generating Random Numbers Visual C++ Programming 55  A random number  Selected from a range of values  Each value has same likelihood of selection  Requires system-defined random number object (Random)  Starting point should be different each time the program runs  Use DateTime variable milliseconds since midnight  Next method generates an integer within a specified range  Two parameters (first, last)  The value will be any integer from first up to (but not including, last

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Finding the Largest Value Visual C++ Programming 58  Use variable to store the largest value  Initialize variable to a small value  For positive integers initialize large to 0  Loop body  Generate new value  Compare value in large to new value  If value in large < new value then replace it with the new value

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Counting Specific Values Visual C++ Programming 61  Initialize a counter to 0 before the loop  Loop body  Produce a new value  If the value is countable then increment the counter

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Nested Loops Visual C++ Programming 65  One loop within the loop body of another  Outer loop  Inner loop  The inner loop executes many times, each time starting anew  Example:  Producing a table (rows and columns)  After completion of the inner loop a “\r\n” is used (newline character)

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Summary Visual C++ Programming 68  User-controlled repetition Used in general solutions involving user interaction  Repetition control structures Used to automate the repetition process Types of loops Pre-test loops, entrance condition Post-test loops, exit condition

Summary (continued) Visual C++ Programming 69 While loop Pre-test Processing continues indefinitely until the pre-test evaluates to false Do…while loop Post-test Processing continues indefinitely until the post-test evaluates to false For loop Built-in loop control variable Processing is usually counter controlled Update is automatic, at the end of each iteration

Summary (continued) Visual C++ Programming 70  Common uses for loops Formula translation - accumulating a sum Accumulating a product Building a string Generating random numbers Finding the largest/smallest value Counting specific values Nested loops