ft_rrange — Reverse Integer Range

Allowed functions: malloc

It must allocate (with malloc()) an array of integers, fill it with consecutive values that begin at end and end at start (including start and end!), then return a pointer to the first value of the array.

int     *ft_rrange(int start, int end);

Examples

• With (1, 3) you will return an array containing 3, 2 and 1.
• With (-1, 2) you will return an array containing 2, 1, 0 and -1.
• With (0, 0) you will return an array containing 0.
• With (0, -3) you will return an array containing -3, -2, -1 and 0.

Solution

Download ft_rrange.c

#include <stdlib.h>

int *ft_rrange(int start, int end) {
	int len, step;

	if (start <= end) {
		len = end - start + 1;
		step = -1;
	} else {
		len = start - end + 1;
		step = 1;
	}

	int *arr = malloc(sizeof(int) * len);
	if (!arr)
		return NULL;

	int i = 0;

	while (i < len) {
		arr[i] = end + (i * step);
		i++;
	}
	return arr;
}

How It Works

Goal: Allocate and return an array of consecutive integers from end to start (reverse of ft_range).

Approach: Calculate length and a reversed step direction, allocate memory, then fill starting from end.

Step by step:

1. Compute the array length from the difference between start and end.
2. Set step to -1 when start <= end (filling backwards from end down) or 1 otherwise.
3. Allocate the array with malloc and fill it using arr[i] = end + (i * step).

Key concept: Reverse filling logic — the step direction is inverted compared to ft_range, so the array starts at end and moves toward start.