How to resize image without changing aspect ratio of the images?

I have collection 100 images. Each image is of different size and I want to make all images of the same size with changing aspect ratio. How to do it?

[KSSV]

Read about imresize

[Adam]

If they don't start out as the same aspect ratio then it is impossible to make them all the same size without changing aspect ratio. If they do all start with the same aspect ratio then surely it is just trivial?

[Jan]

@anu: In the title you want "without" changing the aspect ratio, in the body it is "with". Please clarify this.

[sanakhan]

B = imresize(A,[numrows numcols]) no of rows and columns can be selected according to aspect ratio.

Try [NaN NaN] if you want to preserve the aspect ratio as that of input image or select rows & cols of your own choice.