Unveiling Hidden Gems in the C Programming Language

Many of us encounter the C language during our early semesters in Engineering or IT programs, and some of us continue to use C in our daily work. In this post, I’d like to highlight some intriguing features of C that you might not be aware of:

Multiple Indices in the for Statement

Among all the operators in C, the comma , is often overlooked and rarely discussed in books and tutorials. However, it has a remarkable use when it comes to the for statement, allowing you to have multiple indices.


/* reverse: reverse string s in place */
void reverse(char s[])
  int c, i, j;
  for (i = 0, j = strlen(s)-1; i < j; i++, j--) {
    c    = s[i];
    s[i] = s[j];
    s[j] = c;

Note: Commas used within function arguments are not the same as the comma operator.

Emphasis on Static and Extern Variables

C provides four types of Storage Classes: auto, register, static, and extern.


In C, the static keyword is used to limit the scope of a variable or function to the containing file. This means that identifiers declared as static won’t be accessible in code defined in another file.

When you need to retain the value stored in a local variable across multiple calls to a function, you can qualify a local variable as static. If not defined explicitly, static variables are initialized with zero, and you can only initialize them with constants.

static int var = 10; // Valid
static int var = someFuncReturningConstant(); // Invalid

Since it’s a local variable, you cannot directly access it by name from another function; you must return a pointer to it. Static variables are declared and initialized only once, but their lifespan extends until the thread/process ends.

Static variables are stored in the data segment of memory, unlike regular function variables, which are stored in the stack segment.


In contrast to the static keyword, extern is used to declare a variable without allocating memory. After declaring a variable as extern, you cannot initialize it; you must define it elsewhere in your code.

For function declarations, they are implicitly considered extern. However, for variables, you need to explicitly use the extern keyword.

Some Useful Links

Discovering these lesser-known aspects of C can enhance your programming skills and help you leverage the language’s full potential.