Looping over arrays, printing both index and value

I want to do something like this:

foo=( )
foo[0]="bar"
foo[35]="baz"
for((i=0;i<${#foo[@]};i++))
do
    echo "$i: ${foo[$i]}"
done
# Output:
# 0: bar
# 1: 

Then i tried to loop through it using for in:

foo=( )
foo[0]="bar"
foo[35]="baz"
for i in ${foo[@]}
do
    echo "?: $i"
done
# Output:
# ?: bar
# ?: naz

but here I don't know the index value.

I know you could something like

foo=( )
foo[0]="bar"
foo[35]="baz"
declare -p foo
# Output:
# declare -a foo='([0]="bar" [35]="baz")'

but, can't you do it in another way?

You would find the array keys with "${!foo[@]}" (reference), so:

for i in "${!foo[@]}"; do 
  printf "%s\t%s\n" "$i" "${foo[$i]}"
done

Which means that indices will be in $i while the elements themselves have to be accessed via ${foo[$i]}

you can always use iteration param:

ITER=0
for I in ${FOO[@]}
do  
    echo ${I} ${ITER}
    ITER=$(expr $ITER + 1)
done

INDEX=0
for i in $list; do 
    echo ${INDEX}_$i
    let INDEX=${INDEX}+1
done

In bash 4, you can use associative arrays:

declare -A foo
foo[0]="bar"
foo[35]="baz"

# for Zsh, change this to: for key in "${(k)foo[@]}"
for key in "${!foo[@]}"
do
    echo "key: $key, value: ${foo[$key]}"
done

# output
# $ key: 0, value bar.
# $ key: 35, value baz.

In bash 3, this works (also works in zsh):

map=( )
map+=("0:bar")
map+=("35:baz")

for keyvalue in "${map[@]}" ; do
    key=${keyvalue%%:*}
    value=${keyvalue#*:}
    echo "key: $key, value $value."
done