Deleting Duplicates in array and replacing them with unused values - c

Question

My objective for this program is to let the user determine the size of the array and dynamically allocate memory for whatever size they choose. Once the user defines the size of the array, random numbers that do no exceed the size of the array are placed into all of the allotted positions. Where I am having issues is removing duplicates from the array and replacing them with a value that is not being used,
Example:
Please enter the size of the array:
User Input: 5
Output of code: 5, 3, 3, 1, 2
I would need it to be something like this:
Please enter the size of the array:
User Input: 3
Output of program: 3, 1, 2
Currently reading "C Programming - A Modern Approach" by K.N. King (Second Edition).
if someone could point me in the right direction on how to approach this, it would be much appreciated.Here is my code thus far.
#include <stdio.h>
#include <stdlib.h>
#define true 1
#define false 0
typedef int bool;
int main() {
int *UserData;
int TempPost;
int replace;
int UserInput;
int i;
int result;
bool digit_seen[UserInput];
int digit;
srand ((unsigned) time(NULL));
printf("Please enter the size of the array using a whole number: \n");
scanf("%d", &UserInput);
UserData = malloc(sizeof(int) * (UserInput ) +1);
for(i=0; i < UserInput; i ++) {
result = (( rand() % UserInput) + 1);
}
// check for duplicate values while putting values in array
while(UserInput>0){
digit = UserInput % UserInput;
if(digit_seen[digit])
break;
digit_seen[digit] = true;
UserInput /= UserInput;
if(UserInput > 0)
printf("Repeated digit \n");
else
printf("No repeated digit \n");
}
// Sorting the array using a Bubble sort
while(1){
replace = 0;
for (i=0; i<(UserInput - 1); i++){
if(UserData[i]>UserData[i+1]){
TempPost = UserData[i];
UserData[i] = UserData[i+1];
UserData[i+1] = TempPost;
replace = 1;
}
}
if(replace==0){
break;
}
}
printf("%d \n", result);
return 0;
}

Answer 1

It's not the most efficient way, but you can do it as you're generating the random numbers. When you pick a random number, go through all the previous elements of the array and see if it's already been used. Keep looping until you pick an unused number.
for (i = 0; i < UserInput; i++) {
do {
result = ( rand() % UserInput) + 1;
} while (in_array(result, UserData, i-1));
UserData[i] = result;
}
int in_array(int val, int* array, int array_size) {
for (int i = 0; i < array_size; i++) {
if (array[i] == val) {
return 1;
}
}
return 0;
}
A slightly more efficient way to do it is to initialize the array to 0. Then instead of picking random numbers, pick a random index to fill in, and repeat this until you pick an index that contains 0.
UserData = calloc(UserInput, sizeof(int));
for (i = 1; i <= UserInput; i++) {
int index;
do {
index = rand() % UserInput;
} while (UserData[index] != 0)
UserData[index] = i;
}

Answer 2

What you can do is shuffle the array instead. Just fill the array with all the numbers in order using a simple for loop, then shuffle it with something like this:
//read user input
//create array and fill with all the numbers in order
//[0,1,2,3,4,5 .. ... ]
int index, temp;
// size is the size of the array
for(int i = 0; i < size; i++)
{
index = rand()%size;//random place to pick from
temp = array[i];
array[i] = array[index];
array[index] = temp;
}
This is a lot more effecient -and less error prone- than your current approach.