Closures and Higher-Order Functions

Closures and Higher-Order Functions

In this lesson — part of Advanced Features — you'll learn closures and higher-order functions in C and why it matters in real work.

Why it matters

Functions that take or return functions unlock concise, composable code.

Key ideas

• Functions as values
• map / filter / reduce
• Callbacks
• Composition

In practice

Here's how it looks in idiomatic C:

#include <stdio.h>

int square(int x)  { return x * x; }
int is_even(int x) { return x % 2 == 0; }

int main(void) {
    int src[] = { 1, 2, 3, 4, 5, 6 };
    int out[6], k = 0;
    for (int i = 0; i < 6; i++)            /* filter */
        if (is_even(src[i])) out[k++] = square(src[i]); /* then map */
    for (int i = 0; i < k; i++) printf("%d ", out[i]);
    putchar('\n');
    return 0;
}

C note: C has no built-in map/filter, but functions are first-class via function pointers, so you pass int (*f)(int) to a loop to get the same effect.

Try it yourself

Exercise: In C, use map and filter to get the squares of the even numbers.

Recap

You now understand closures and higher-order functions and can apply it in C. Mark this lesson complete and continue to the next one.