I need to make a project in C++(not very big) in my college....can you suggest me some good ideas....

I was thinking of implementing 10-15 algorithms with their complete complexity description

can u give me some other ideas

This just came out of the blue... But how about card games?
Poker, gin rummy, fifty-two pickup (if you're good at graphics and want to tick people off by making it modal and disabling all capacity to close it...)

Simulations are always good. Develop a simple predator/prey model that ends when all predators are dead or all prey is gone, have the computer figure out a ratio that will usually gives a balance, or has the longest duration.

That'll be a challenge in and of itself, but not too bad.

For extra fun, make it a 3d playing field, add prey/predator orientations/awareness, and go insane.

Or maybe it'd be better to start on something to kill all humans first.

I liked the ideas....but i know about basic graphics commands in c++(in-built).....for better graphics i guess i need to use some kinda library....can u suggest some good library...which can be easy to learn and implement...i was thinking about opengl but i know nothing about windowsprogramming

Neither do I, I'm afraid. I'm just throwing out ideas. For the simulation, however, you could do an fprintf of occupied entries in a 2d array to a text file, then reconstruct each step on an overhead or something.
Not pretty, but it'd work.

you dont need to know windows api to use opengl. its independant of windows. The only time you need windows coding is if you want your opengl app to run in a window instead of full screen.
theres excellent opengl tuts here

If you don't want to go graphic how about extending the vector STL class to handle mathematical vectors/matrices. Or how about writing code to implement a B-tree.