Intro. 4002-208 to Prog. [in C++] Day 09 More on Repetition
Objectives
Review while loop for loop Auto increment operator Accumulator Compound operator
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Review of while loop
while (loop condition) { loop body } Loop condition is a Boolean condition. Execute loop body if loop condition is true.
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Use a Sentinel Loop
//read first input value while (input is invalid) { //execute code //read another input value }
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Finger work
Run the program grades.cpp Add a data validation loop to ensure score is between 0 and 100, inclusively.
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for loop
Most common use is to execute the loop body a specific number of times Basics
Initialize counter Test counter halt loop when test is false Change counter for(initialize counter; test counter; change counter)
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Perform code a specific number of times
for ( int counter = 1 ; counter <= number_of_times ; counter=counter+1 ) { //code to repeat }
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Print 1 to 10
Initialize counter: int k = 1 Test counter: k<=10 Change counter: k=k+1 for (int k=1; k<=10; k=k+1) { cout << k << endl; }
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Counter
Numeric variable used for counting. Examples
Number of test scores Number of employees
Declare as type int as the count is a whole number. If counter declared in for statement, local in variable loop body only.
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Finger work
Print 1 up to 25 Print -5 up to 5 Print even numbers from 0 up to 40 Print 10 down to 0 Read in number of times that loop is to be execute, that is, 1 to number of times
Run the program for the number of times 5, 10, 1, 0, -5
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Auto increment
The update part of for statement is k=k+1 The operator ++ is auto increment, that is, add one to an integer variable. k=k+1 is the same as k++ (generally) Technically, this is post increment as ++ is placed after the variable Pre increment ++k In for statement, both work the same.
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Accumulator
A variable that adds up a set of numbers, here scores. Format: sumScores = sumScores + score; Add the current value of sumScores to score and store the sum back into the variable sumScores Acts like the total on a cash register.
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Finger work
Back to grades.cpp Read in the number of grades to be entered. Compute and print the average of the scores.
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Compound Operators
sumScores = sumScores + score; equivalent to sumScores += score; Does not require the programmer to type the accumulator variable name twice.
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More Compound Operators
+= -= *= /= %/ x += 5; x -= b; x *= c + 2; x /= 5; x %= 5; x = x + 5; x = x b; x = x * (c + 2); x = x / 5; x = x % 5;
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