bash shell nested for loop

#!/bin/bash
# loop*figures.bash

for i in 1 2 3 4 5  # First loop.
do
    for j in $(seq 1 $i)
    do
        echo  -n "*" 
    done
    echo 
done
echo
# outputs
# *
# **
# ***
# ****
# *****

for i in 5 4 3 2 1 # First loop.
do
    for j in $(seq -$i -1)
    do
        echo  -n "*" 
    done
    echo 
done

# outputs
# *****
# ****
# ***
# **
# *

for i in 1 2 3 4 5  # First loop.
do
    for k in $(seq -5 -$i)
    do
        echo -n ' '
    done
    for j in $(seq 1 $i)
    do
        echo  -n "* " 
    done
    echo 
done
echo

# outputs
#     * 
#    * * 
#   * * * 
#  * * * * 
# * * * * * 

for i in 1 2 3 4 5  # First loop.
do
    for j in $(seq -5 -$i)
    do
        echo  -n "* " 
    done
    echo 
    for k in $(seq 1 $i)
    do
        echo -n ' '
    done
done
echo

# outputs
# * * * * * 
#  * * * * 
#   * * * 
#    * * 
#     *


exit 0

On one line (semi-colons necessary):

for i in 0 1 2 3 4 5 6 7 8 9; do for j in 0 1 2 3 4 5 6 7 8 9; do echo "$i$j"; done; done

Formatted for legibility (no semi-colons needed):

for i in 0 1 2 3 4 5 6 7 8 9
do
    for j in 0 1 2 3 4 5 6 7 8 9
    do 
        echo "$i$j"
    done
done

There are different views on how the shell code should be laid out over multiple lines; that's about what I normally use, unless I put the next operation on the same line as the do (saving two lines here).

The question does not contain a nested loop, just a single loop. But THIS nested version works, too:

# for i in c d; do for j in a b; do echo $i $j; done; done
c a
c b
d a
d b