i do not understand why the for loop runs twice, the first value to be printed should be 2 and the last value should be 16 and not 4 since 4 is still less than 10
i have done a for loop that increments the initial value by one but i have not tried to increment the initial value by multiplying it by the first value
for (int i = 2; i <10; i = i*i) {
System.out.println(i);
}
i expected it to run 4 times but it ran just two times
Your loop is equivalent to this:
int i = 2; // Initializer
while (i < 10) // Condition
{
System.out.println(i);
i = i * i; // Update part
}
Note how it will never enter the body of the loop when i is 10 or greater - so it will never print 16.
In other words, the execution looks like this:
Set i to 2.
Check: is i less than 10? Yes, so enter the body of the loop.
Print i.
Set i = i * i, so it's now 4.
Check: is i less than 10? Yes, so enter the body of the loop.
Print i.
Set i = i * i, so it's now 16.
Check: is i less than 10? No, so finish.
Finding what your code is doing is easy with a paper sheet and a pen...
first run, i = 2 -> i < 10 == true -> print 2
second run, i = 2*2 = 4 -> i < 10 == true -> print 4
third run, i = 4*4 = 16 -> i < 10 == false -> out
I try to explain how works for.
1) You initialized variable i = 2
2) Check i < 10
3) Print(i) = 2
--- NEXT ----
1) i = i*i (2*2) = 4
2) Check i < 10 = 4<10 = true
3) Print(i) = 4
--- NEXT ----
1) i = i*i (4*4) = 16
2) Check i < 10 = 16<10 = false
3) EXIT
First time i = 2, loop ran
second time i = 4, loop ran
third time i = 16, loop failed => break
Welcome to stackoverflow. For these cases you should learn to debug your code for better self understanding
You are squaring. 2,4,16 but 16 is greater than i<10 so it does not do that
Because of i = i*i
i = 2
1. i = 2*2 = 4 (4 < 10)
2. i = 4 * 2 = 8 (8 < 10)
3. i = 8 * 2 = 16 (16 > 10)
Related
This code print the prime factors of a number.
I wanted to know how does it print the same Prime Factor twice
eg: 45 => 3.3.5
// get the number
for(int i = 2; i< number; i++) {
while(number%i == 0) {
System.out.println(i+" ");
number = number/i;
}
}
if(number >2) {
System.out.println(number);
}
The easiest/best way to understand what the code is doing is to run through it. You could try using a debugger on your end, but we can also try to summarize here:
i = 2
nothing happens, because 45 is not divisible by 2
i = 3
the while loop iterates twice, printing 3 twice, and also setting
number = 45 -> 15 -> 5
i = 4
nothing happens, because 45 is not divisible by 4
i = 5
the while loop iterates once, printing 5 once, and setting number = 5 / 5 = 1
At this point, the outer for loop fails, because i = 5 and number = 1.
when i = 3, while loop iterates two times.
In first iteration it will print 3 and update value of number = 15
As number is updated it will again iterate.
In second iteration it will again print 3 and update value of number = 5
now, (5%3 == 0) is not possible so it will not iterate third time.
So the goal was to use a nested for loop to output 6 rows and 10 columns. The thing was though that the inner for loop was supposed to check to see whether the number was even or odd as, if it was even, we would add 2 to it and then print out that number 10 times before moving onto the next output. So this is what were were supposed to get
1 1 1 1 1 1 1 1 1 1
4 4 4 4 4 4 4 4 4 4
3 3 3 3 3 3 3 3 3 3
6 6 6 6 6 6 6 6 6 6
5 5 5 5 5 5 5 5 5 5
8 8 8 8 8 8 8 8 8 8
I thought I was on the right track but my output is a complete mess, here's what I have. Thank you to anyone willing to help.
for (int numberE = 1; numberE <= 6; numberE++)
{
for (int nestedE = 1; nestedE < 10; nestedE++)
{
if (numberE%2 == 0)
{
numberE += 2;
System.out.printf("%2d", numberE);
} else {
System.out.printf("%2d", numberE);
}
}
System.out.printf("%2d\n", numberE);
}
well to start with your inner loop will only iterate nine times. second you don't need a nested loop, you need one loop and a guard determining when to print.
Don't modify numberE inside the loops. Instead just print numberE + 2.
Also, if your inner loop runs from 0 to <10 you will get 10 iterations and you don't need to print the number again - just a newline.
for (int numberE = 1; numberE <= 6; numberE++)
{
for (int nestedE = 0; nestedE < 10; nestedE++) // <-- start at 0 and end <10 for 10 iterations
{
if (numberE%2 == 0)
{
System.out.printf("%2d", numberE + 2); // <-- print the number + 2
} else {
System.out.printf("%2d", numberE);
}
}
System.out.println(); // <-- don't print the value again here
}
I would do it this way. Gives the required result.
public class NestedForLoop {
public static void main(String[] args) {
for (int i = 1; i <= 6; i++)
{
int temp = i;
if(temp%2 == 0) {
temp +=2;
}
for(int j=1;j<=10;j++) {
System.out.print(temp+" ");
}
System.out.println();
}
}
}
A brief description of what is happening here:
So, since we need 6 rows, we use the value of 6 as a row counter. The variable i takes care of keeping a count of the rows. Here since the target is 6, we start from row number 1 and go until row no 6. Inside each value of the loop, we save the value of i to temp because we don't want the value of i to change before incrementing in the main for loop. We then check if this temp value is even by doing a modulo division by 2. If it is even, we increment the temp value by 2.
Then, we run a loop from 1 to 10 since we need 10 columns to print the value temp(either the original i or incremented because it was even). After exiting the loop, finally to move to the next row, we do a System.out.println().
I would suggest using a temporary variable to store the current intended value.
The issue with your solution was that you were modifying the value of numberE by using numberE += 2; inside the second for loop, this changes the value globally.
Moving the final column in to the nested for loops also makes it easier as you wouldn't need to define the temporary variable outside of the loop. Using this also meant changing the <10 to <=10.
for (int numberE = 1; numberE <= 6; numberE++) {
for (int nestedE = 1; nestedE <= 10; nestedE++) {
int current = (numberE % 2 == 0) ? numberE + 2 : numberE;
System.out.printf("%2d", current);
}
System.out.printf("\n");
}
You were pretty close though, with practise you'll get better.
I understand how mostly everything works in a loop in Java but I came to a realization that I am failing to understand one thing which is The Order a Loop Operates.
Basically I am failing to understand this because of this simple but boggling piece of code that was displayed in my class, the code is displayed below.
public class Test {
public static void main (String[] args) {
int sum = 0;
for (int k = 1; k < 10; k += 2)
{
sum += k;
System.out.print(sum + " ");
}
}
}
The output the program puts out is 1 4 9 16 25
Now I understand how it repeats and spits out the numbers but how does it go about even creating 1. Now you can say it created 1 by taking k and adding it to sum but shouldn't k be equaling 3?
It goes k = 1; This sets k equal to 1. k < 10; Checks if k is less than 10. Then the question is when k += 2; Shouldn't k now equal to 3 but instead sum is now somehow equal to 1 after this operation occurred of adding 2 to 1, 2 + 1 = 3 but 3 + 0 = 1? How does this even go about.
My rationalizing for this is that any program I thought was to interpret code line by line or uniformly and not jumping around.
Overall my question is, how is sum equal to 1 when k is actually equal to 3.
The sections of the for loop are run at different times.
The first section is run once at the start to initialize the variables.
The second is run each time around the loop at the START of the loop to say whether to exit or not.
The final section is run each time around the loop at the END of the loop.
All sections are optional and can just be left blank if you want.
You can also depict a for loop as a while loop:
for (A;B;C) {
D;
}
is the same as:
A;
while (B) {
D;
C;
}
Let's step through your code:
We setup an int with initial value of 0 and assign it to sum.
We setup a for loop, setting int k = 1, and we will loop while k is less than 10, and after each iteration, 2 will be added to k.
So, the first iteration, k = 1. sum currently equals 0, so sum += k is actually 0 = 0 + 1 = 1. There's the 1 you are getting.
For the second iteration, k = 3. sum currently equals 1, so sum += k is actually 1 = 1 + 3 which is 4. There's the 4 that is showing up.
Repeat this for the rest of the loop!
In the first iteration of the loop, k=1. The k+=2 is only run at the beginning of the next iteration of the loop. The loop variable update condition (the last part of the for loop - i.e. the k+=2 part) never runs on the first iteration but does run on every other one, at the start. Therefore what you have is:
Iteration 1:
k=1
sum = 0 + 1; //so sum = 1
Iteration 2:
k=1+2 // so k=3
sum = 1 + 3 // so sum = 4
Iteration 3:
k=3+2 //k=5
sum = 4 + 5 //sum=9
etc...
It goes like this:
Initialize (k = 1)
Check condition (k < 10) (stop if false)
Run the code in the loop (sum += k and print)
Increment (k += 2)
Repeat from step 2
Following this logic, you get that 1 is printed first.
The last condition, k += 2 occurs after the first iteration of the loop.
So it's
k = 1, sum = 1
k = 3, sum = 4
k = 5, sum = 9
k = 7, sum = 16
k = 9, sum = 25
k is only incremented after the loop iteration. In general for any loop the values are updated after a loop iteration so k goes 1,3,5,7,9 and so the sum is correct.
Oh believe I had same problem. And you have to understand this quickly because when you are going to start doing bubble sort it will confuse you even more.
The thing you need to understand is that, its that it doesnt actually add +2 to 'k' until its done reading whats inside your 'for loop'
So this is how it starts, its starts with what you set 'k' for which is 1.
k = 1 is it less than 10? Yes, then do whats in the 'for loop' . Sum at first was initiated to 0. then in the first loop we add the value of k to whatever sum already has. So
sum = 0, k = 1. Therefore 0 +1 = 1. then next line ouput the value of sum with space. AND here is the IMPORTANT PART, it has now reach the end of the loop. So now it will add +2 to the value that k already has.
So k = 1 + 2 = 3. And now we start the second loop.
k=3, is less than 10? yes, ok do whats in for loop. add k to whatever value that sum already has. Sum is = 1 right ? and k is now equal to 3 right？ So 3 + 1 = 4. And it display sum with a space and it has reach the end of the for loop so it add +2 to k that already has 3 in it which will equal to 5. and the loop continues.
oouff hope that helps! So remember it adds +2 at the end of the loop. Sorry if theres some typos typing from my samsung kinda annoying a bit cuz i have japanese keyboard...
Good luck！
has to
Let's break up your code. The keyword for just means loop. It will start # 1 and continue as long as k is less than 10. It will also increase by k+=2. To translate, it means k = k +2
Inside the loop sum = sum + k. It will then print the value that sum has plus a space.
k = 1, sum = 1
k = 3, sum = 4
k = 5, sum = 9
k = 7, sum = 16
k = 9, sum = 25
and keep repeating. Let me know if you still have trouble grasping this concept
How to print the following output with only one for-loop in java?
1 2 3 4 5 6 7 8 9 1 0 9 8 7 6 5 4 3 2 1
Code snippet:
class Series{
public static void main(String args[]){
for(int i=1; i<=10; i++){
System.out.println(i);
}
System.out.println(i);
for(int j=9; j>=0; j--){
System.out.println(j);
}
}
My program's in the following manner. Can anyone correct it?
public static void main(String...strings ){
int dir = 1;
for(int i=1; i>0; i+=dir){
if(i == 10)
dir = -1;
System.out.print(i+" ");
}
}
Output:
1 2 3 4 5 6 7 8 9 10 9 8 7 6 5 4 3 2 1
The series in the question is wrong.
It should be: 1 2 3 4 5 6 7 8 9 10 9 8 7 6 5 4 3 2 1
The code, in one loop, is as follows:
int ctr = 1;
for(int i = 1; i > 0; i += ctr)
{
if(i == 10)
{
ctr = -1;
}
System.out.print(i + " ");
}
Every sequence follows a pattern, Let's try finding one in this.
To work with this code, analyze What loop would print with the variable that you increment and What you want in the output?
In your problem, assuming that the number you are entering is entered by user i.e. n, you want 2*n - 1 numbers in your sequence. Hence we now have the limits of our loop
For n=5, Under no Conditions the loop would simply print a sequence like this
1 2 3 4 5 6 7 8 9 provided you are starting your loop from 1.
The sequence you want is 1 2 3 4 5 4 3 2 1.
Now looking at both the sequences you can see that the sequence is same till the mid point that is till the value of n is reached. Now if you observe the pattern further if you subtract 2 from 6 you get 4 that is the number you want in your sequence. Similarly when you subtract 4 from 7 you get 3 which is the next number in the sequence you required.
Hence the pattern this sequence follows is that after the loop reaches the value provided by the user you need to subtract (2 * k) from the next number where k starts from 1 and increases with every iteration
Now you know how to achieve the pattern which would be easy to achieve using conditional statements.
PS: let's assume an added constraint of using no conditional statements then we have to write an arithmetic expression to solve our problem.
Following the pattern again the expression must display i where i is the variable incremented in the loop
so our code looks like
for (i = 1; i<=2*n - 1;i++)
{
System.out.print(i);
}
Now to get the pattern we need to subtract multiples of 2 after the user provided integer n is reached. But whatever we subtract should also not affect out first n integers.
Since we know we have to subtract multiples of 2 we know the expression we have to subtract would look like 2 * (____). As we want a sequence of multiples we can obtain that using %. As soon as the number goes over n the % operator on i would give us back sequence from 0 to n-1 hence generating multiples of 2.
Now our expression comes to 2 * (i % n). But the problem is that it would also subtract from the first 4 integers which we don't want so we have to make changes such that this expression will work only after loop reaches the value provided by the user.
As we know the division / operator provides us with the quotient. Hence it would yield us 0 till we reach the value of user defined number and 1 for the rest of the sequence as we run our loop till 2*n -1. Hence multiplying this expression to our previous expression yields 2*(i%n)*(i/n)
And there we have it our final code to generate the sequence would be
for (int i = 1;i<2*r;i++)
{
System.out.print(i - 2 * (i%r)*(i/r));
}
Observe the above code for the first n-1 integers i/r would make subtracted expression 0 and for i = n, i % r would make the expression 0. For the rest of the sequence i / r would generate value 1 and hence we will get multiples of 2 from 2 *( i % r) to provide us with the sequence
try this
int j = 10;
for (int i = 1; i <= 10; i++) {
if(i<10)
System.out.print(" " +i);
if(i==10){
i--;
System.out.print(" " +j);
if(j==1){
i++;
}
j--;
}
}
OutPut
1 2 3 4 5 6 7 8 9 10 9 8 7 6 5 4 3 2 1
Something like this?
for(int i=0;i<20;i++) {
if((i/10)%2 == 0)
System.out.print(i%10 + " ");
else
System.out.print((10-(i%10)) + " ");
}
Try this code, You just need a if condition in for loop.
int i = 1;
for(int j=1; j<=20; j++)
{
if(j<11)
System.out.print(j+" ");
else
{
System.out.print((j - i == 10 ?" ": (j-i + " ")));
i = i+2;
}
}
public class forLoopTest {
public static void main(String[] args) {
for (int i = 1; i < 10; i++) {
System.out.print(i + " ");
}
for (int j = 10; j >= 1; j--) {
System.out.print(j + " ");
}
}
}
int i = 1;
int j = 1;
while (i < 4) {
j += i;
i++;
}
System.out.println("i = " + i);
System.out.println("j = " + j);
I have the following above and I am trying to figure out how it works. I am new to java so I do not know how to debug my code yet. The output of this program says that i = 4 and j = 7. However the condition of the while loop should only execute when i < 4. Why does it execute when i = 4? I tried changing the condition to i <= 4 and it outputs i = 5. What am I missing here?
The loop counter will be incremented for every iteration through the loop. When the counter has been incremented past 3 (when it's equal to 4) the loop will stop. The loop won't run when the counter is 4, but the counter was still incremented to 4
i = 1
is 1 less than 4? Yes, so loop.
add one to i so now i = 2.
is 2 less than 4? Yes, so loop.
add one to i so now i = 3.
is 3 less than 4? Yes, so loop.
add one to i so now i = 4.
is 4 less than 4? No, leave the loop.
Print the value of i which is 4.
You enter the loop when i=3. Inside the loop, you increment i by 1 (i++). At the end of that iteration, you check if i<4, which it is not, because i=4.