C Program - Shifting Elements in an array

Question

"Write a program that allows a user to input an integer for the size of an array. Using Malloc is recommended. Randomly generate an integer for each element of the array. Next, creating a funcion to rotate the array. Rotation of the array means that each element is shifted right or left by one index, and the last element of the array is also moved to the first place"

Example: 31 83 91

Which direction to shift and how many times?- Left

How many times would you like to shift? 2

End Result: 91 31 83

Currently my code. It's not shifting.

#include <stdio.h>
#include <stdlib.h>

int main(){

int i, temp, swapped;
int SlotNumber;
int *ptr;
char direction;
int ShiftAmount;

printf("How many slots would you like in your array?\n");
scanf("%d", &SlotNumber);
for(i=0;i<SlotNumber;i++){
    printf("%d \t", rand());
}
ptr = (int *)malloc(SlotNumber*sizeof(int));

printf("\nWhich direction would you like to shift it to? R/L?\n");
scanf(" %c", &direction);
printf("\nHow many times would you like to shift?\n");
scanf("%d", &ShiftAmount);

if((direction=='R')||(direction=='r')){
    while(1){
        swapped = 0;
        for(i=0;i<ptr+1;i++){
            if(ptr[1]>ptr[i+ShiftAmount]){
                int temp = ptr[i];
                ptr[i] = ptr[i+ShiftAmount];
                ptr[i+ShiftAmount] =temp;
                swapped = 1;
            }
        }
        if(swapped == 0);
        break;
    }
}
printf("\nNewList\n");
for(i=0;i<ptr;i++){
    printf("%d \t",ptr[i]);
}

return 0;
}

1) you don't fill the ptr array with anything. 2) You just need to shift the elements. You don't care what their values are, so there is no reason to check whether an element's value is greater than another element's value. You do, however, need to check whether the new position is inside the bounds of the array and take appropriate action if it is not. — FredK
– FredK, Commented Feb 5, 2016 at 21:49
The text says that you have to shift by 1 element. Yet the example asks the user for "how many times" they want to shift. So essentially this is a shift by n elements. Shifting by n elements is a more generic and more interesting problem than shifting by 1. So, what is actually required? Shift by 1 or shift by n? Or is it required to implement shift by n through consecutive shifts by 1? — AnT stands with Russia
– AnT stands with Russia, Commented Feb 6, 2016 at 18:08

gmoniava · Accepted Answer · 2016-02-05 22:41:28Z

1

There were few problems with your code. Here is improved solution with left shift, right shift I leave to you.

#include <stdio.h>
#include <stdlib.h>
#include <time.h>


int main()
{

    int i, j;
    int SlotNumber;
    int *ptr;
    int ShiftAmount;
    int temp;

    srand(time(NULL));

    printf("How many slots would you like in your array?\n");
    scanf("%d", &SlotNumber);

    ptr = malloc(SlotNumber*sizeof(int));

    // Fill array with random numbers
    for(i=0;i < SlotNumber; i++)
    {
        ptr[i]=rand();
        printf("%d \t",ptr[i]);

    }

    printf("\nHow many times would you like to shift?\n");
    scanf("%d", &ShiftAmount);


    for(i=0; i < ShiftAmount; i++)
    {
        temp = ptr[0];
        for(j=0;j < SlotNumber - 1;j++)
        {
            ptr[j] = ptr[j+1];
        }
        ptr[SlotNumber - 1]=temp;
    }

    printf("\nNewList\n");
    for(i=0; i < SlotNumber; i++)
    {
        printf("%d \t",ptr[i]);
    }

    free(ptr);

    return 0;
}

edited Feb 5, 2016 at 22:41

answered Feb 5, 2016 at 21:54

gmoniava

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2 Comments

EGTech Over a year ago

Thank you. I added the print statement to ask the user the shift direction, and I was able to get it to shift to the right as well.

gmoniava Over a year ago

@EGTech nice to hear that

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