Higher-Order Functions (Passing a Function Pointer as an Argument)

This lesson covers passing a function pointer as an argument in C, so you can treat logic itself as a component. It's for anyone searching "C function pointer usage."

Passing another function's address (a function pointer) as an argument is called a higher-order function. It's like "specifying only the method to use, and leaving the actual work to whoever receives it."

The example's bubbleSort() function takes a function pointer, int (*cmp)(int, int), as an argument, calling cmp() for every comparison. Passing a different function, compareDescending(), achieves a descending sort.

A common early mistake is the syntax for declaring a function pointer. The distinctive form, return-type (*variableName)(parameter-type-list), can feel confusing at first.

In real projects, designing with function pointers as callbacks is an important technique for achieving flexible, swappable logic in C.

📖 Reference code

#include <stdio.h>

int compareDescending(int a, int b) {
    return b - a;
}

void bubbleSort(int arr[], int n, int (*cmp)(int, int)) {
    for (int i = 0; i < n - 1; i++) {
        for (int j = 0; j < n - i - 1; j++) {
            if (cmp(arr[j], arr[j + 1]) > 0) {
                int tmp = arr[j];
                arr[j] = arr[j + 1];
                arr[j + 1] = tmp;
            }
        }
    }
}

int main(void) {
    int nums[] = {5, 2, 8, 1};
    bubbleSort(nums, 4, compareDescending);
    for (int i = 0; i < 4; i++) {
        printf("%d", nums[i]);
        if (i < 3) printf(", ");
    }
    printf("\n");
    return 0;
}

✍️ Your code

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🧪 This site can't compile or run C directly, so it checks on the spot whether what you typed matches the reference code (scoring happens entirely in your browser — nothing is sent anywhere).