Should I Learn C or C++?

The question comes up quite often, "Should I bother to learn C, or go straight to C++?" Many beginning programmers wonder if it's worth it to spend the time learning C, when they know a more advanced language is readily available. Others wonder if they're going to be missing out on anything important if they skip C, and proceed directly to C++ without passing Go or collecting $200.

While it is true that well-written C code will normally compile under C++, C is not a proper subset of C++. There are a few differences that can make a valid C program invalid in C++. The easiest examples to illustrate involve the addition of keywords such as new and class to C++, which were not reserved words in C. The following (contrived) valid C program will not compile as C++.

int main(void) {
 int class, new; // both class and new are C++ keywords
 printf("Enter two integers > ");
 scanf("%d %d", &class, &new);
 printf("The two numbers are: %d  %d\n", class, new);
 printf("Their sum is %d\n", class + new);
}

Another difference that's often cited between C and C++ is that C supplies an implicit cast when a void pointer is assigned to a pointer of a specific type, while C++ requires an explicit cast. The following valid C code will not compile using C++:

void* ptr;
int *i = ptr;

In order to make this code valid C++, an explicit cast to an int pointer must be supplied:

void* ptr;
int *i = (int *) ptr;

While it's important to understand that C and C++ are really two separate languages, it's just as important to understand that the parts of C that aren't valid C++ are extreme edge cases. C++ was originally intended to be just an extension of C (Stroustrup started out calling it C with Classes), so an effort was made to ensure that valid C syntax was broken in only a very few places. As Scott Meyer points out in Effective C++, C++ is really a federation of related programming languages: C, Object-Oriented C++, Template C++, and the STL. Almost all valid C programs will compile as C++, with very little, or often no changes necessary.

Most programmers who are deliberating between learning either C or C++ should probably skip C and learn C++. Start out with a book like C++ Primer and you will learn good programming style, not only in the C subset, but in all of the parts of the C++ language. Unless you plan on doing some work on the Linux kernel or another project that you know uses C, the only thing you will be really missing by not learning C first is Kernighan & Ritchie's C Programming Language. You can always go back and read K&R after you've taught yourself good C++ style and habits.


Further Reading

Wikipedia, Compatibility of C and C++.