如何从较大的矩阵中提取2x2子矩阵

I am a very basic user and do not know much about commands used in C, so please bear with me...I cant use very complicated codes. I have some knowledge in the stdio.h and ctype.h library, but thats about it. I have a matrix in a txt file and I want to load the matrix based on my input of number of rows and columnsI am a very basic user and do not know much abo