Homework & Coursework Questions

1. The problem statement, all variables and given/known data:

Write a shell script that finds and display the sum of even positive integers from 0 to 100. Use the while control structure. Show your script and a sample run.

2. Relevant commands, code, scripts, algorithms:

Must us a while loop

3. The attempts at a solution (include all code and scripts):

This is one attempt:

Code:

for i in {0..100}
do
        (( b = $i % 2 ))
        if [ $b -ne 0 ]
        then
        echo $i
fi
done

Another attempt, just trying to get somewhere and have it print something, but with this one I was getting a syntax error..

Code:

sum=0
while (( i=0; i<=100; i++ ));do
        if (( $i % 2 )); then
        echo $i is odd
else
        echo %i is even
fi
done

Portland Community College, Portland, OR, United States, Shawli Sengupta, CS-140U-0-14858 - Intro to UNIX/Linux
I cannot add the URL to the course because I do not have enough post on this forum.

Hi Nastybutler,
What does this line mean?

Code:

echo %i is even

--- Post updated at 11:11 ---

Missing space in this line after ;

Code:

while (( i=0; i<=100; i++ ));do

correct string

Code:

for ((i=0; i<=100; i++)); do

--- Post updated at 11:21 ---

You just make out your mistakes, do not copy mindlessly please

Code:

for i in {0..100}; do
        b=$(( $i % 2 ))
        if [ $b -ne 0 ]; then
                echo $i
        fi
done

Did you read the answers to your other thread attentively? They mentioned the "step" parameter of the for command - you might try to adapt it to your problem?
And, you might want to read the man page of your shell to learn about the correct syntax of the (mandatory to your problem) while statement - as you used it, the shell will issue a "syntax error".

What shell are you using for your class assignment?

What do your class notes, your text book, or the manual page for your shell say is the proper format for a while loop? Since your assignment says you have to use a while loop, that would seem to be a good place to start (especially since neither of your coding attempts contains a while loop that isn't getting a syntax error).

Note that the syntax for a while loop is not the same as the syntax for a for loop. And, the script that you are writing does not need two loops. If you need to use a while loop, you do not need a for loop to get the job you are trying to do done.

As a hint, I would say that if you're using a while loop to solve this problem, anything using {1..100} is probably not going to help. Using that construct does not fit with the syntax of a while loop. And, after reading your other thread, I would comment that when you said you didn't know how to add numbers that weren't supplied as input from a user, you were wrong. The statement in your previous thread:

Code:

        sum=$((sum + $n))

did exactly that. Neither sum nor n were provided by a user, but you have a statement that is adding two numbers together when neither of those numbers were typed in by a user. This statement, or one very similar to it, is likely to be needed in your script. It doesn't contain any syntax errors and it does add two numbers together and store the updated results correctly.

Hi Nastybutler...

Your OP suggests you 'must us[e] a while loop', therefore a for loop is not required at this point.
This is pseudocode, see if you can adapt it.

Code:

shebang needed to call your shell required

assign_a_COUNTer_to_zero
assign_my_SUM_a_starting_point_of_zero

while test[ing] against the 100 limit
do
    do your arithmetic here which uses both SUM and COUNT
    optional, print each line if you want to here to see how it is doing
    increase your COUNTer by your needed amount
done
print your final value here and should equal the last line of you optional listing

EDIT:
And thoroughly read Don's post...

Instead of incrementing the counter by 1 in the loop and then testing if it even, you could also increment the counter by 2 at every iteration. That way you would not need to test if it is even if the initial value of the counter is even.

We are using this in the bash shell. Sorry I'm very new with this so I don't have the syntax down 100%.

--- Post updated at 07:08 AM ---

After everyones feedback this is what I have so far. Please bare in mind again, I'm still learning and I know it's not perfect.

Code:

#!/bin/bash

counter=0
sum=0

while [[ $counter -le 100 ]]
do
        echo -n "$counter"
if ! [ $((counter % 2)) -eq 0 ]
then
        echo "$sum"
        sum=((sum + $counter))

fi
done

I am getting an error message that reads:

Code:

./count4.sh: line 14: syntax error near unexpected token `fi'
./count4.sh: line 14: `fi'

Moderator's Comments:

Please remember to use CODE tags when displaying sample input, sample output, and code segments.