Transforming an Array (map-like Logic)

This lesson covers transforming every element of an array in C, so you can implement map-like logic. It's for anyone searching "C array transformation implementation."

C has no built-in map() function like some other languages, but you can achieve the same thing by filling a new array inside a for loop. Think of it like a conveyor belt that processes every item passing through the same way.

The example's doubleArray() function processes the original array, nums — received as a pointer — one element at a time, writing the results into a separate array, result. Notice that in C, an array is passed to a function as a pointer.

A common early mistake is not preparing the result array ahead of time. Since there's no automatically-resizing array like in some other languages, you need to reserve an array of sufficient size beforehand.

In real projects, this pattern is used for bulk data transformation — applying sales tax to a price, converting units, and more.

📖 Reference code

#include <stdio.h>

void doubleArray(int *nums, int *result, int n) {
    for (int i = 0; i < n; i++) {
        result[i] = nums[i] * 2;
    }
}

int main(void) {
    int nums[] = {1, 2, 3};
    int doubled[3];
    doubleArray(nums, doubled, 3);
    for (int i = 0; i < 3; i++) {
        printf("%d", doubled[i]);
        if (i < 2) 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).