CODEWITHSUNDEEP
carrays
Wanze
Wanze

Reputation: 11

Segfault error in array sorting algorithm in C

I'm a beginner to programming and I'm working through K.N.King's "C Programming: A Modern Approach". Right now I'm trying to do programming project 1 of chapter 9 but I keep getting a segfault and I'm not sure what's wrong with the code. Any correction is appreciated!

These are the instructions:

Write a program that asks the user to enter a series of integers (which it stores in an array), then sorts the integers by calling the function selection_sort. When given an array with n elements, selection_sort must do the following:
1. Search the array to find the largest element, then move it to the last position in the array.
2. Call itself recursively to sort the first n - 1 elements of the array.

And this is my code:

#include <stdio.h>

void selection_sort(int n, int a[n]);

int main(void)
{
    int n;

    printf("Number of integers to sort: ");
    scanf("%d", &n);

    int a[n];

    printf("Enter the integers: ");
    for (int i = 0; i < n; i++) {
        scanf("%d", &a[i]);
    }

    selection_sort(n, a);

    printf("Sorted array: ");
    for (int i = 0; i < n; i++)
        printf("%d", a[i]);

    return 0;
}

void selection_sort(int n, int a[n])
{
    int swap, max = a[n - 1];

    for (int i = 0; i < n; i++) {
        if (a[i] > max) {
            max = a[i];
            swap = a[n - 1];
            a[n - 1] = max;
            a[i] = swap;
        }
    }
    if (n > 1)
        selection_sort(n - 1, a);
}

EDIT: changed while (n > 1) to if (n > 1) and now it works perfectly. But why wouldn't it work with while?

Upvotes: 1

Views: 83

Answers (2)

Gaurav Sehgal
Gaurav Sehgal

Reputation: 7542

You need to have some base condition for recursion to avoid endlessly calling the same function.You can do something like

void selection_sort(int n, int a[])
{
    if(n<=0)return;  //base condition
    int swap, max = a[n - 1];

Upvotes: 2

Roland Illig
Roland Illig

Reputation: 41686

You need a condition for not calling selection_sort. As it is now, your selection_sort always calls selection_sort, which results in an endless loop.

And, since you decrement n at each step, at one point it becomes negative, and you start accessing a[-1], which is wrong.

Upvotes: 3

Related Questions