Here is, How you can install composer from command prompt and access by composer command in WINDOWS 7.

Go to php.exe located folder. if you are using WampServer, probably

"C:\wamp\bin\php\php5.5.12\"

press and hold CTRL + SHIFT together and right click inside folder, and select "open command window here ".



Copy and paste this code in CMD.

php -r "readfile('https://getcomposer.org/installer');" | php


If everything's fine, it will show message like,
"

#!/usr/bin/env php
All settings correct for using Composer
Downloading...
Composer successfully installed to: C:\wamp\bin\php\php5.5.12\composer.phar
Use it: php composer.phar

"



you can see composer.phar file in same folder.


Go to C:/ drive and create a folder named composer

Move downloaded composer.phar to that folder.


Create composer.bat file in same folder and copy below contents to that file.

@ECHO OFF
php "%~dp0composer.phar" %*

create composer file. without any extensions, you can do this by opening CMD in this folder and typing type NUL > composer without Quotes.

and drag that  file to your text editor, preferably notepad++ . and paste below contents.

#!/bin/sh
dir=$(d=$(dirname "$0"); cd "$d" && pwd)
# see if we are running in cygwin by checking for cygpath program
if command -v 'cygpath' >/dev/null 2>&1; then
  # cygwin paths start with /cygdrive/ which will break windows PHP,
 # so we need to translate the dir path to windows format. However
 # we could be using cygwin PHP which does not require this, so we
 # test if the path to PHP starts with /cygdrive/ rather than /usr/bin.
 if [[ $(which php) == /cygdrive/* ]]; then
    dir=$(cygpath -m $dir);
   fi
fi
dir=$(echo $dir | sed 's/ /\ /g')
php "${dir}/composer.phar" $*

save.

Now 3 files will be there inside composer folder.

Now, set PATH to composer so we can access composer by just typing composer in CMD.

• Show Desktop.
• Right Click My Computer shortcut in the desktop.
• Click Properties.
• You should see a section of control Panel - Control Panel\System and Security\System.
• Click Advanced System Settings on the Left menu.
• Click Environment Variables towards the bottom of the window.
• Select PATH in the user variables list.
• Append your PHP Path (C:\composer) to your PATH variable, separated from the already existing string by a semi colon.
• Click OK

Finally,
restart computer.
If you dont want to restart computer, there is an alternate way,

Open CMD and copy paste below lines.

taskkill /f /IM explorer.exe
start explorer.exe
exit

Open a new command prompt, and type composer 



Now you should see composer is installed and working properly.

Feel free to be part of discussion.