Setting variable for use later in a case construct - linux

Question

I have this practice problem that is asking me to take my existing code and insert variables for letter grades into the existing 'IF' statements for use in a case construct that reads off a sentence based on the letter grade assigned. The problem I'm having is how to set the variable in the first place, ie. do I need to do a whole new IF/ECHO line for the variable? How do I even word it in the first place?
Would it be something like grade=A?
Here's what I have so far: (EDITED TO INCLUDE SUGGESTIONS)
#!/bin/bash
# Bash shell script to calculate student average
# Usage: ./grade1.sh
# Declare some integer type variables
declare -i test1
declare -i test2
declare -i test3
declare -i test4
declare -i lab
declare -i sum
echo
echo "=================="
echo "Grade Calculator "
echo "=================="
echo
read -p "Enter first name: " firstname
read -p "Enter last name: " lastname
echo
read -p "Enter test score 1: " test1
read -p "Enter test score 2: " test2
read -p "Enter test score 3: " test3
read -p "Enter test score 4: " test4
read -p "Enter lab score: " lab
sum=$test1+$test2+$test3+$test4+$lab
average=$((sum/5))
VAR1=A
VAR2=B
VAR3=C
VAR4=D
VAR5=F
if [ $average -ge 90 ]; then
echo "Course grade: $VAR1"
elif [ $average -ge 80 ]; then
echo "Course grade: $VAR2"
elif [ $average -ge 70 ]; then
echo "Course grade: $VAR3"
elif [ $average -ge 60 ]; then
echo "Course grade: $VAR4"
elif [ $average -le 60 ]; then
echo "Course grade: $VAR5"
fi
echo
echo "Grade results . . ."
echo "Student name: $firstname $lastname"
echo "Total points: $sum"
echo "Course average: $average"
echo
case $grade in
A) echo "An 'A' represents superior course work."
;;
B) echo "A 'B' represents above average course work."
;;
C) echo "A 'C' represents average course work."
;;
D) echo "A 'D' represents below average course work."
;;
F) echo "An 'F' represents failing course work."
;;
esac

Answer 1

The task, as you stated it, doesn't make very much sense .... it would make sense if we have the number of grades and the shresholds completely variable. But, well, it's a practice problem, so they might require you doing some nonsense, just for the exercise.
As it is an exercise, I'll give you some pointers, but don't write down the whole solution.
Assuming that you are really supposed to do what you are asking here (and did not misunderstood the task), you are supposed to replace the literal grades (A, B, C, D, F) by variables. Since you have 5 grades, you need either 5 variables or an array of 5 elements. You asked for variables, so for this exercise, this is the way to go.
Since you have 5 variables, you need to invent 5 different names, for example
this=A
is=B
a=C
silly=D
exercise=F # Note: grade E does not exist
You can write these definition somewhere before they are first used, and feel free to use variable names which suit you better. Now bash knows about these variables, you can use them, for instance:
elif [ $average -ge 60 ]; then
echo "Course grade: $silly"
Now to two things you didn't ask for, but might be interested to know:
First, the calculation of average in your code is incorrect. If you set all tests and the lab to 1, you will get an average of 5 (try it out).
Second, in your case statement, you are using a variable grade, which you don't set anywhere. For example, at the place that you found out that the grade is D (and you did find this out, because you do an echo of this fact), you should set the variable
grade=$silly

Answer 2

This is a circumstance where you can let the shell (bash specifically) help you with your problem by utilizing arrays to help you build your text output and let character classes help with matches in your case statement.
For example, since you know you are grading on the traditional A-F 90-50 breakpoints, you can create several arrays to allow you index all associated information, e.g.
ltrgrades=( A B C D F )
numgrades=( 90 80 70 60 50 )
prefixes=( An A A A An )
comments=( "superior"
"above average"
"average"
"below average"
"failing" )
A function can handle all your output needs per-student by passing the associated index as its first argument:
results() {
echo
echo "Grade results . . ."
echo "Student name : $firstname $lastname"
echo "Total points : $sum"
echo "Course average: $average"
echo
echo "Course grade : ${ltrgrades[$1]}"
echo
echo "${prefixes[$1]} '${ltrgrades[$1]}' represents ${comments[$1]} course work."
}
Utilizing a heredoc simplifies providing multi-line output:
## use a heredoc for multi-line text
cat << EOF
"=================="
"Grade Calculator "
"=================="
EOF
(note: you could utilize a heredoc within the results function)
Finally, you can use character classes as your case matches and '*' to mark the default case, e.g.
case "${average%.*}" in
1?? ) results 0;;
9[0-9] ) results 0;;
8[0-9] ) results 1;;
7[0-9] ) results 2;;
6[0-9] ) results 3;;
* ) results 4;;
esac
Putting it altogether, you could do:
#!/bin/bash
# Bash shell script to calculate student average
# Usage: ./grade1.sh
ltrgrades=( A B C D F )
numgrades=( 90 80 70 60 50 )
prefixes=( An A A A An )
comments=( "superior"
"above average"
"average"
"below average"
"failing" )
results() {
echo
echo "Grade results . . ."
echo "Student name : $firstname $lastname"
echo "Total points : $sum"
echo "Course average: $average"
echo
echo "Course grade : ${ltrgrades[$1]}"
echo
echo "${prefixes[$1]} '${ltrgrades[$1]}' represents ${comments[$1]} course work."
}
## use a heredoc for multi-line text
cat << EOF
"=================="
"Grade Calculator "
"=================="
EOF
read -p "Enter first name : " firstname
read -p "Enter last name : " lastname
echo
read -p "Enter test score 1: " test1
read -p "Enter test score 2: " test2
read -p "Enter test score 3: " test3
read -p "Enter test score 4: " test4
read -p "Enter lab score : " lab
sum=$((test1 + test2 + test3 + test4 + lab))
average=$(echo "scale=2; $sum / 5" | bc)
case "${average%.*}" in
1?? ) results 0;;
9[0-9] ) results 0;;
8[0-9] ) results 1;;
7[0-9] ) results 2;;
6[0-9] ) results 3;;
* ) results 4;;
esac
Example Use/Output
$ bash grades.sh
"=================="
"Grade Calculator "
"=================="
Enter first name : John
Enter last name : Doe
Enter test score 1: 85
Enter test score 2: 93
Enter test score 3: 94
Enter test score 4: 91
Enter lab score : 92
Grade results . . .
Student name : John Doe
Total points : 455
Course average: 91.00
Course grade : A
An 'A' represents superior course work.
$ bash grades.sh
"=================="
"Grade Calculator "
"=================="
Enter first name : Mary
Enter last name : Jane
Enter test score 1: 86
Enter test score 2: 93
Enter test score 3: 72
Enter test score 4: 71
Enter lab score : 77
Grade results . . .
Student name : Mary Jane
Total points : 399
Course average: 79.80
Course grade : C
A 'C' represents average course work.
$ bash grades.sh
"=================="
"Grade Calculator "
"=================="
Enter first name : Sally
Enter last name : Smith
Enter test score 1: 55
Enter test score 2: 61
Enter test score 3: 42
Enter test score 4: 58
Enter lab score : 59
Grade results . . .
Student name : Sally Smith
Total points : 275
Course average: 55.00
Course grade : F
An 'F' represents failing course work.
Since the grades are computed as a floating-point value using bc, you can, and probably should, handle rounding (e.g a 79.5 rounds to 80 while a 79.4 remains 79. You can handle that with another variable score with something similar to:
sum=$((test1 + test2 + test3 + test4 + lab))
average=$(echo "scale=2; $sum / 5" | bc)
fract=${average#*.}
score=${average%.*}
(( ${fract:0:1} >= '5')) && ((score++))
case $score in
1?? ) results 0;;
9[0-9] ) results 0;;
8[0-9] ) results 1;;
7[0-9] ) results 2;;
6[0-9] ) results 3;;
* ) results 4;;
esac
Now Mary Jane's grade with an average of 79.80 is rounded to 80 a B instead of a C. It's up to you to determine how rounding is handled, this is just one way to approach it. You could re-write results to show both the computed average and rounded score, e.g.
results() {
cat << EOF
Grade results . . .
Student name : $firstname $lastname
Total points : $sum
Course average: $average ($score)
Course grade : ${ltrgrades[$1]}
${prefixes[$1]} '${ltrgrades[$1]}' represents ${comments[$1]} course work.
EOF
}