Question

I have an assignment to write a recursive program that gets an array (lets call it arr1), the size of the array (n), and a value(s).
The program will check if there are two numbers in the array so that their summary is s.
example
if the array is {1,3,2,0,5} and s=7, then the function will print “yes” because 5+2=7.
if the array is {1,3,2,0,5} and s=9, then the function will print “no”. no summary of a pair is equal to 9.

My algorithm works like this:
i calculate the summary of the last spot in the array (arr1[n-1]), with every other spot. if i find a couple that their sum is s, great, print yes and leave.
if i dont find, then i do the same, but instead of arr1[n-1] i check arr1[n-2]. i delete the last spot.

Here’s my code:

#include <stdio.h>
#include <conio.h>
#include <stdlib.h>
void input_array_dyn(int* a, int n);
void rec(int* a,int n, int s);
void main()
{
    int n=0,s=0;
    int* a;
    printf("Enter value S\n");
    scanf("%d",&s);
    printf("Enter the size of the array\n");
    scanf("%d",&n);
    a=(int*)calloc(n,sizeof(int));
    printf("Enter %d values for the array\n",n);
    input_array_dyn(a,n);
    rec(a,n,s);
    free(a);
    getch();
}
void input_array_dyn(int* a,int n)
{
    int i=0;
    for(i=0;i<n;i++)
        scanf("%d",a[i]);
}
void rec(int* a,int n, int s)
{
    int i;
    if(n==1)
    {
        printf("There are no 2 number whos summary yields S\n"); 
        return;
    }
    for(i=0;i<n-1;i++)
    {
        if(a[n-1]+a[i]==s)
        {
            printf("There are two numbers that give s\n");
            return;
        }
    }
    rec(a,n-1,s);
}

I get an error saying: “Unhandled exception at 0x5846e30e (msvcr100d.dll) in Test.exe: 0xC0000005: Access violation writing location 0x00000000.”

also: Does anyone have a better idea for an algorithm to do this? 🙂

Answer 1

In input_array_dyn():

scanf("%d", a[i]);

You’ve forgotten a &.