loopless

first use a function

function sevenc
{


if [ ! -e "$1" ]; then #check if the file exist
    echo "File $1 does not exist" #if not exist print echo output
else
    sed -i -e 's/- /-/g' "$1" #remove space on the first 10 values
    awk '{print $7}' "$1" > /tmp/$(basename $1.txt)_S.txt #print the column number 7 and copy the output in a file
    rm "$1"  #remove old file
fi
}

• when the shell recognize a function, it will pass argument (if any to $1 $2 ... and so on).
• by the way

's/- /-/g' "$1" #remove space on the first 10 values

NO, it turn all space- to - on the line, be there 1, 4, 10 or 255.

then no need for more var

sevenc /tmp/1wall_long.txt
sevenc /tmp/1wall_test1.txt
sevenc /tmp/1wall_test2.txt
sevenc /tmp/1wall_test3.txt
sevenc /tmp/3mt_long.txt
sevenc /tmp/3mt_OpenSpace_test1.txt
sevenc /tmp/3mt_OpenSpace_test2.txt
sevenc /tmp/3mt_OpenSpace_test3.txt
sevenc /tmp/3rooms_test1.txt
sevenc /tmp/3rooms_test2.txt
sevenc /tmp/3rooms_test3.txt
sevenc /tmp/20mt_OpenSpace_test1.txt
sevenc /tmp/20mt_OpenSpace_test2.txt
sevenc /tmp/20mt_OpenSpace_test3.txt

(provided you have no more use of fileXX var).

loopless (sol. 2)

should you want to pass more argument, and using Terdon's optimisation try

function eight
{

file=$1
destdir=${2-/tmp} # use second arg if defined, else /tmp
exten=${3-S} 

if [ ! -e "$file" ]; then #check if the file exist
    echo "File $file does not exist" #if not exist print echo output
else
    sed  -e 's/- /-/g' "$file" \
    awk '{print $7}' "$1" > /"$destdir"/$(basename $1.txt)_"$exten".txt #print the column number 7 and copy the output in a file
    rm "$file"  #remove old file
fi
}

to be called with

eight /tmp/1wall_test3.txt /my/projec/dir T ## will use /my/project/dir as dit, T as extension
eight /tmp/1wall_test1.txt /my/project ## will use /my/project as dir
eignt /tmp/1wall_test2.txt ## will use default value

those function can be defined in .bashrc and be use interactively.

with loop

while read f
do
if [ ! -e "$f" ]; then #check if the file exist
    echo "File $1 does not exist" #if not exist print echo output
else
    sed -i -e 's/- /-/g' "$f" #remove space on the first 10 values
    awk '{print $7}' "$f" > "/tmp/$(basename $f .txt)_S.txt" #print the column number 7 and copy the output in a file
    rm "$f"  #remove old file
fi
done <<EOF
/tmp/1wall_long.txt
/tmp/1wall_test1.txt
/tmp/1wall_test2.txt
/tmp/1wall_test3.txt
/tmp/3mt_long.txt
/tmp/3mt_OpenSpace_test1.txt
/tmp/3mt_OpenSpace_test2.txt
/tmp/3mt_OpenSpace_test3.txt
/tmp/3rooms_test1.txt
/tmp/3rooms_test2.txt
/tmp/3rooms_test3.txt
/tmp/20mt_OpenSpace_test1.txt
/tmp/20mt_OpenSpace_test2.txt
/tmp/20mt_OpenSpace_test3.txt
EOF

You can use an array of files and loop over it with for:

#!/bin/bash

files=(/tmp/1wall_long.txt
       /tmp/1wall_test1.txt
       /tmp/1wall_test2.txt
       /tmp/1wall_test3.txt
       /tmp/3mt_long.txt
       /tmp/3mt_OpenSpace_test1.txt
       /tmp/3mt_OpenSpace_test2.txt
       /tmp/3mt_OpenSpace_test3.txt
       /tmp/3rooms_test1.txt
       /tmp/3rooms_test2.txt
       /tmp/3rooms_test3.txt
       /tmp/20mt_OpenSpace_test1.txt
       /tmp/20mt_OpenSpace_test2.txt
       /tmp/20mt_OpenSpace_test3.txt )

for file in "${files[@]}" ; do
    if [ ! -e "$file" ]; then
        echo "File $file does not exist"
    else
        sed -i -e 's/- /-/g' "$file"
        # Use parameter expansion to create the new file name.
        newfile=${file%.txt}_S.txt
        awk '{print $7}' "$file" > "$newfile"
        rm "$file"
    fi
done

Personally, I would avoid hardcoding the file names. That is rarely a good idea and it is usually better to have the option of passing target files as arguments. Additionally, you are modifying the file in place and then deleting the original. That's not efficient, just modify the file on the fly and print the 7th column without having to write it to disk. For example:

#!/usr/bin/env bash

## Iterate over the file names given
for file in "$@"; do
    ## Get the output file's name. The ${file%.*} is
    ## the file's anme without its extension.
    outfile="${file%.*}"_S.txt
    ## If the file exists
    if [ -e "$file" ]; then
    ## remove the spaces and print the 7th column
    sed 's/- /-/g' "$file" | awk '{print $7}' > "$outfile" &&
        ## Delete the original but only if the step
        ## above was successful (that's what the && does)/
        rm "$file" 
    else
    ## If the file doesn't exist, print an error message
    echo "The file $file does not exist!"
    fi
done

Then, you can run the script like this:

foo.sh /tmp/1wall_long.txt /tmp/1wall_test1.txt /tmp/1wall_test2.txt /tmp/1wall_test3.txt /tmp/20mt_OpenSpace_test1.txt /tmp/20mt_OpenSpace_test2.txt /tmp/20mt_OpenSpace_test3.txt /tmp/3mt_long.txt /tmp/3mt_OpenSpace_test1.txt /tmp/3mt_OpenSpace_test2.txt /tmp/3mt_OpenSpace_test3.txt /tmp/3rooms_test1.txt /tmp/3rooms_test2.txt /tmp/3rooms_test3.txt 

If you do want to have the names hard coded, just use an array as suggested by @choroba:

#!/usr/bin/env bash

files=(/tmp/1wall_long.txt /tmp/1wall_test1.txt /tmp/1wall_test2.txt /tmp/1wall_test3.txt /tmp/20mt_OpenSpace_test1.txt /tmp/20mt_OpenSpace_test2.txt /tmp/20mt_OpenSpace_test3.txt /tmp/3mt_long.txt /tmp/3mt_OpenSpace_test1.txt /tmp/3mt_OpenSpace_test2.txt /tmp/3mt_OpenSpace_test3.txt /tmp/3rooms_test1.txt /tmp/3rooms_test2.txt /tmp/3rooms_test3.txt )


## Iterate over the file names given
for file in "${files[@]}"; do
    ## Get the output file's name. The ${file%.*} is
    ## the file's anme without its extension.
    outfile="${file%.*}"_S.txt
    ## If the file exists
    if [ -e "$file" ]; then
    ## remove the spaces and print the 7th column
    sed 's/- /-/g' "$file" | awk '{print $7}' > "$outfile" &&
        ## Delete the original but only if the step
        ## above was successful (that's what the && does)/
        rm "$file" 
    else
    ## If the file doesn't exist, print an error message
    echo "The file $file does not exist!"
    fi
done