C vs C++: Review

We pause one final time at the end of the semester to look at differences that have popped up between C and C++.

As a reminder of the differences we've already covered:

• Compiling
  • Compiler is gcc not g++
  • Files are named .c not .cpp
  • Included libraries are different (C includes stdio.h and stdlib.h)
• Input/Output & Variables
  • printf instead of cout
  • scanf instead of cin
  • FILE* instead of ifstream
  • There is no string nor bool type
• Arrays and Memory Allocation
  • C++ uses new, but C must use malloc or calloc
  • C strings are just char arrays.

Today we'll look at functions, and linked lists. The summary is actually pretty easy:

• Functions
  • No function overloading in C.
• Structs and Lists
  • Structs must say "struct" in front of the type.
  • Otherwise all the same!

Functions

You cannot overload functions in C. Recall that overloading is the ability to write two functions with the same function name but different function signatures. This is a very useful thing to do. For example, you might want two max functions:

int max(int, int);
int max(int, int, int);

Structs

Just a syntax change! Structs are actually a C construct. C++ builds on structs with something called classes, but we ran out of time to introduce those. The change here is syntactic, and frankly a little annoying. You now have to write struct in front of all your type declarations.

Example code: a linked list

• C++ program: Here's a C++ program that reads a linked list of strings from the user (stop at END) and print it: ex.cpp.
• C program: Below is the C code that works the same as ex.cpp. Observe that struct Node is always used instead of Node.

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

struct Node 
{
  char data[128];
  struct Node* next;
};

// Adds to the front!
struct Node* add2front(char* val, struct Node* L);
// Recursive, prints it backwards!
void printList(struct Node* L);
// Deletes a list
void deleteList(struct Node* L);

int main()
{
  struct Node* mylist = NULL;

  char s[128];
  while( scanf("%s", s) == 1 && strcmp(s, "END") != 0 )
    mylist = add2front(s, mylist);

  printList(mylist);
  deleteList(mylist);
  return 0;
}

// Adds to the front!
struct Node* add2front(char* val, struct Node* L) 
{
  struct Node* T = malloc(sizeof(struct Node));
  strcpy(T->data, val);   // ***NOTE HERE***
  T->next = L;
  return T;
}

// Recursive, prints it backwards!
void printList(struct Node* L) 
{
  if ( L != NULL )
  {
    printList(L->next);
    printf("%s\n", L->data);
  }
}


// Deletes a list
void deleteList(struct Node* L)
{
  if( L != NULL )
  {
    deleteList(L->next);
    free(L);
  }
}

Mandatory Practice Problem

Sample runs

$ ./a.out
Enter alpha: 185112
RAINEL NUNEZ
$ ./a.out
Enter alpha: 200000
No Mid with that alpha was found!