The C Programming Language by Kernighan & Ritchie, AKA (K&R) is a good historical document, but NOT a book you should use to learn the language! It is NOT a Standard. It was superseded by the official ANSI & ISO Standards, C89/90, C99, C11, C17, and the upcoming, C2x Standards! Too much has been changed, added, and/or deleted!
Short of taking a course in C Programming from a qualified instructor, you need to study a good book on the C Programming Language, cover to cover, and do all the exercises at the end of each chapter! Choose one of the three listed below:
C Programming, A Modern Approach, 2nd Edition
Author: K. N. King
C Primer Plus, 6th Edition
Stephen Prata
C How to Program, 8/e
Deitel & Deitel
Studying one of these books, and writing code, you will have a much better understanding of the current C Programming language.