CSCI 235 — diff C Java 2

Our reference

• Chapters 7 to 12 of An Introduction to the C Programming Language and Software Design
• a pretty good reference from Univerity of Illinois at Urbana-Champaign

A review

• Fall 2015 CSCI 255 notes on C vs Java.
• int main(int argc, char *argv[]) { }
• System.out vs stdout vs std::cout with << and std::iomainip
• System.in vs stdin vs std::cin with >> and std::iomainip
• C is not object oriented
• C does not have try / catch — You must test return values!

Chapter 7 — Pointers

• Draw elements of the following types
  • int *
  • char *
  • int **
  • void *
• Two new operators
  • unary & — address-of
  • unary * — dererence
  • study examples on page 50
• Examples of assigning to pointers and pointing to pointers
• The const declaration modifiers
  • const int* pA ;
  • int const* pB ;
• call by reference (vs call by value)
  • Let’s write an integer swap routine
  • C++ reference variables
  • strtol man page — look at the example!
• NULL in C is similar to null in Java.
• passing a function with pointers
  • C qsort vs Java sort
• Scary examples in Fall 2011 ECE 209 notes

Chapter 8 — Arrays and Strings

• Size of array is usually set in declaration
  • until you get to Chapter 9
• If P is an array of integers, then P is a constant pointer to an integer.
• Pointer arithmetic — The following rules formally apply only when the pointers address lvalues within the same array.
  • P[i] is *(P+i).
  • If P is a pointer to an integer, then P+i is a pointer to the i’th integer after the integer referenced by P.
  • If P is a pointer to an integer, then P-i is a pointer to the i’th integer before the integer referenced by P.
  • P++ increments P to point to the next integer in the array.
  • P-- decrements P to point to the previous integer in the array.
  • An odd collection: P--, P++, P < Q, P == Q, P <= Q, P >= Q, P += 5, P - Q.
  • The address of the non-existent element one past the end of the array can be used in comparisons. This is weird stuff.
• A hack to find the number of elements — sizeof(P)/sizeof(*P). Only works for static arrays.
• Strings are null terminated char arrays
• C string library
• arrays of pointers vs multidimensional array
• Problem 16 of Fall 2016 CSCI 255 final

Chapter 9 — Dynamic Memory

Concentrate on sections 9.1—9.3: We are skipping the CSCI 202 stuff.

• Memory regions of C
• malloc and friends
  • in C

           int *X ;
           X = (int *) malloc(n * sizeof(int)) ;
           if (X == NULL) …
         

  • in C++

           int *X ;
           X = new int[n] ;
           if (X == NULL) …
         

• There is no garbage collection in C — use free

Chapter 10 — The C Preprocessor

• Fall 2009 ECE 209 C Preprocessor notes
• Try: gcc -E pointers.c > pointers.c-after-cpp

Chapter 11 — Structures and Unions

• A C struct is a Java class with only public fields — no methods
• A C union is strange, but useful
  • /usr/include/netinet/ip.h vs IP4 header
  • /usr/include/netinet/ip_icmp.h vs ICMP header
• Fall 2011 ECE 209 structure notes (with linked lists). We used to do this in CSCI 202. See Problem 4 in Spring 1994 CSCI 202 final.
• Fall 2011 ECE 209 union examples

Chapter 12 — Bitwise Operators

We do this in Chapter 2 of the textbook.

• Bitwise operators: Just like in Java except there is no >>>
  • C’s signed >> is like Java’s >>
  • C’s unssigned >> is like Java’s >>>
• Bitwise logical operators have a lower precedence than relational operators: x & b == c is x & (b == c)
• Bit-fields are used in the IP and ICMP headers