wrong output in sort + find bigges in Array

Question

Today I created a program which have 3 Functions:

sortArray(array,length);
removeDuplicateInArray(array, length);
max = findMax(array, length);

The program works fine but, if I run it more times let say, three times, the output is only one OK, other two is different and i think that somehow has to do with the length of the array in findMax function, because i remove duplicates and the array does not have the same size . I'm not sure if there is the problem.

The program is this:

#include<stdio.h>

void sortArray(int *array, int length){
    int i, j, k, temp;

    for(i=0;i<length-1;i++){
        for(k=0;k<length-i-1;k++){
            if(array[k]<array[k+1]){
                temp=array[k];
                array[k]=array[k+1];
                array[k+1]=temp;
            }
        }
    }

    for(j=0;j<length;j++){
        printf("%d ",array[j]);
    }
    printf("\n\n");
}

void removeDuplicateInArray(int *array, int length){
    int i,j,k;

    for (i = 0; i < length; i++) {
      for (j = i + 1; j < length;j++) {
         if (array[j] == array[i]) {
            for (k = j; k < length; k++) {
               array[k] = array[k + 1];
            }
            length--;
         }else{
            j++;
         }
      }
   }

   for (i = 0; i < length; i++) {
      printf("%d ", array[i]);
   }
   printf("\n\n");
}

int findMax(int *array, int length){
    int i;
    int max = array[0];

    for(i=1;i<length;i++){
        if(max == array[i]){
            continue;
        }

        if(max<array[i]){
            max = array[i];
        }
    }
    return max;
}

int main(void){
    int array[] = {-9,-7,-3,-1,9,7,3,1,-8,-6,-4,-10,-2,8,6,4,2,5,-5,-10};
    int length = sizeof array / sizeof array[0];
    int max;

    sortArray(array,length);
    removeDuplicateInArray(array, length);
    max = findMax(array, length);

    printf("Max = %d\n", max);
    return 0;
}

and the output is:

michi@michi-laptop:~$ ./program 
9 8 7 6 5 4 3 2 1 -1 -2 -3 -4 -5 -6 -7 -8 -9 -10 -10 

9 8 7 6 5 4 3 2 1 -1 -2 -3 -4 -5 -6 -7 -8 -9 -10 

Max = 9
michi@michi-laptop:~$ ./program 
9 8 7 6 5 4 3 2 1 -1 -2 -3 -4 -5 -6 -7 -8 -9 -10 -10 

9 8 7 6 5 4 3 2 1 -1 -2 -3 -4 -5 -6 -7 -8 -9 -10 

Max = 9
michi@michi-laptop:~$ ./program 
9 8 7 6 5 4 3 2 1 -1 -2 -3 -4 -5 -6 -7 -8 -9 -10 -10 

9 8 7 6 5 4 3 2 1 -1 -2 -3 -4 -5 -6 -7 -8 -9 -10 

Max = 2034093120
michi@michi-laptop:~$ ./program 
9 8 7 6 5 4 3 2 1 -1 -2 -3 -4 -5 -6 -7 -8 -9 -10 -10 

9 8 7 6 5 4 3 2 1 -1 -2 -3 -4 -5 -6 -7 -8 -9 -10 

Max = 912874208
michi@michi-laptop:~$ ./program 
9 8 7 6 5 4 3 2 1 -1 -2 -3 -4 -5 -6 -7 -8 -9 -10 -10 

9 8 7 6 5 4 3 2 1 -1 -2 -3 -4 -5 -6 -7 -8 -9 -10 

Max = 1269451840
michi@michi-laptop:~$ ./program 
9 8 7 6 5 4 3 2 1 -1 -2 -3 -4 -5 -6 -7 -8 -9 -10 -10 

9 8 7 6 5 4 3 2 1 -1 -2 -3 -4 -5 -6 -7 -8 -9 -10 

Max = 1946221408
michi@michi-laptop:~$ ./program 
9 8 7 6 5 4 3 2 1 -1 -2 -3 -4 -5 -6 -7 -8 -9 -10 -10 

9 8 7 6 5 4 3 2 1 -1 -2 -3 -4 -5 -6 -7 -8 -9 -10 

Max = 9

The output should be 9, but the output is not always 9

Answer 1

The removeDuplicateInArray function changes the length of the array, but the calling function, main in your case, doesn't know about the new length.

You can either return the new length from the function:

int removeDuplicateInArray(int *array, int length)
{
    // code as above

    return length;
}

and call it like this:

length = removeDuplicateInArray(array, length);

or you can pass the length as a pointer, which will reflect the canges:

void removeDuplicateInArray(int *array, int *plength) ...
{
    int length = *plength;

    // use and modify length as above

    *plength = length;
}

and call it like this:

removeDuplicateInArray(array, &length);

I prefer the second variant, because it doesn't allow you to accidentally forget about the return value.

The garbage value you see is shifted in from beyond the array's bounds, because you loop up to k < length and access athe element at index k + 1, which might be length, which is one element beyond the array.

Answer 2

In removeDuplicateInArray pass the length by pointer so it will have the proper value later in the main void removeDuplicateInArray(int *array, int *length).