Shell Programming and Scripting

Hello,
Im trying to work on a small script for a formula converting temperatures, Celsius to fahrenheit.

I have a formula, and it works.... it works every way I try it. But it keeps giving me the wrong results every time with expr.

The formula for C to F would be:
divide by 5, multiply by 9, add 32.

So..... simple code here

Code:

read c
f= `expr $c / 5 \* 9 + 32`
echo $f

The problem is, its never correct because expr can't seem to add the decimals right.

For instance 32 degrees celcius.
f=`expr 32 / 5 \* 9 + 32` gives me 86 for some reason. It should give 89 (or 89.6)

I have also tried it another way, which seems odd, but still should give correct results.

Code:

f=`expr 9 / 5 \* $c + 32`

Again, I have tested, it should be 89, but it ends up giving me 64.


Because expr 9 / 5 is giving me 1, instead of 1.8
So 1 * 32 = 32 + 32 = 64.
It should be 1.8 * 32 = 57.6 + 32 = 89.6

It seems like my problem is the fact that expr won't account for decimals.
Is there a way to get it to acknowledge the decimals?
Or is this not possible with the expr command?

Thanks a lot

I think expr does not work with floating point number. Try awk instead:-

Code:

echo | awk ' { printf "%0.2f\n", (57.6 + 32); } '

Or use bc

Code:

echo "scale=2; 57.6 + 32" | bc

expr does not "do" floating point numbers (decimal numbers).

Code:

bc -l

does.

Code:

 echo "1.356 * 1.2" | bc -l

The awk command does double precision (15 digits of floating point) as well.

Code:

echo "13 14.112" | awk '{print $1 * $2}'

Thanks a lot,

Im having some trouble with bc too.

Code:

echo $c / 5 \* 9 + 32 | bc
echo 32 / 5 \* 9 + 32 | bc

gives me 86 (instead of 89)

Im not sure how it is rounding 89.6 to 86..... its making no sense to me

adding the -l

Code:

echo 32 / 5 \* 9 + 32 | bc -l

gives me 89.600000000000000000
Which is correct. But for the output file, I just need the whole number. (89)

You have to use scale to get accurate results. Here is what is happening:-

See the difference in results with scale and without scale:-

Code:

echo '( 32 / 5 )' | bc
6
echo '( 32 / 5 ) * 9 ' | bc
54

Code:

echo 'scale=2; ( 32 / 5 )' | bc
6.40
echo 'scale=2; ( 32 / 5 ) * 9' | bc
57.60

I hope you understood how 89.6 got rounded to 86

That explains it......
Now I see why it rounded it like that......

but even if I do a scale=1, I get 89.6
scale=0 obviously gives me the rounded "86"

So is there not a way to just get 89?

Code:

 
$ res=$(echo 32 / 5 \* 9 + 32 | bc -l); 
$ echo ${res%%.*}
89