Adel Notes Week 4 (Chapter 4)

Question 1

loops

Answer 1

to iterate and have something repeated. Each loop has three parts: initialization, condition, and update.

Question 2

While-loop

Answer 2

runs until a condition returns false

	while(condition){ …//body of the loop }

Question 3

Do-while loop

Answer 3

runs the body of the loop once and then starts checking the condition(post-test); body gets executed at least once.

do{
…//body of the loop
}while(condition);

Question 4

For-loop

Answer 4

<> an entry-controlled loop that is used to execute a block of code repeatedly for the specified range of values. Basically, for loop allows you to repeat a set of instructions for a specific number of iterations.

for(initialization; condition; update){
//body
}
for(int i = 100; i>=0; i–){

…//body of the loop
}

Question 5

Notes

Answer 5

● Missing update can result in infinite loops. Make sure your loop condition returns false at some point to prevent the crashing of your program.

● Don’t add semi-colon after the condition parenthesis. This can result in infinite loop that will crash the program.
Ex:
while(7<10);

● Use for loop when you know how many times the body of the loop should repeat.

● Use do-while or while loop for data-validation. Get the data from the user. If invalid ask again until valid.

● Variable we make inside a loop are local and get destroyed when the loop ends.
Ex:
for(int i=0; i<=5;i++){
System.out.println(i);
}
System.out.println(i); // error

Question 6

Are variables inside a loop or condition statement like if-statements, not locals? If so, can they be accessed?

Answer 6

variables defined inside a loop or condition statement like if statement are local and cannot be accessed outside the loop or conditional statement. It would result in an error.

Question 7

Break

Answer 7

break keyword closes the loop.

    for(int i=1; i<=10;i++){
        if (i == 6)break;
else System.out.print(i); //12345
    }
    System.out.println(i);

Question 8

Continue

Answer 8

It moves on to the next iteration.

for(int i=1; i<=10;i++){
if (i == 6)continue;
else System.out.print(i); //1234578910
}

Question 9

Running totals

Answer 9

running total is a variable that accumulates overtime.

ex: total = total + sale;

Question 10

Counter

Answer 10

to keep track of a number of times something has happened. Usually starts at 0 and Increments as needed.
Ex:
double totalSales = 0.0;
int numSales = 0;
int userInput ;
while(moreSales){
//get user input
…
if(userInput == sentinel) {
moreSales = False; //to signal when to stop.
break;
}
numSales++; //increment counter
totalSales += userInput;
}

Question 11

Sentinel value

Answer 11

a value to stop the loop. used to notify the program to stop acquiring input.

For example, while entering positive numbers, a sentinel value might be -1, or while entering names, a sentinel value might be done, end, or quit.

We usually use a sentinel value when we don’t know the exact number of iterations in a loop.

Question 12

Data Validation/Input Validation

Answer 12

make sure the data user inputs is what is expected and won’t crash the program. One common way is to use do-while loop or while loop and repeat while the input is invalid.
ex:
int numSales;

//the following makes sure the user doesn’t input negative values.
do{
cin&raquo_space; numSales;
}while(numSales < 0)