C Exercises: Rearrange positive and negative numbers alternatively in a given array

Last update on March 18 2025 13:23:14 (UTC/GMT +8 hours)

93. Rearrange Positive & Negative Numbers Alternately

Write a program in C to rearrange positive and negative numbers alternatively in a given array.

N.B.: If positive numbers are more they appear at the end and for also negative numbers, they too appear in the end of the array.

Expected Output:
The given array is:
-4 8 -5 -6 5 -9 7 1 -21 -11 19
The rearranged array is:
-4 7 -5 1 -21 5 -11 8 -9 19 -6

The task is to write a C program that rearranges the elements of a given array such that positive and negative numbers alternate. If there are more positive or negative numbers, the extra numbers will appear at the end of the array. The program should iterate through the array to reorganize the elements accordingly and then display the rearranged array.

Sample Solution:

C Code:

#include <stdio.h>

// Function to swap two numbers in an array
void changeNumber(int *arr1, int i, int j) 
{
    int temp = arr1[i];
    arr1[i] = arr1[j];
    arr1[j] = temp;
}

// Function to split positive and negative numbers in the array
void splitPosNeg(int *arr1, int size)
{
    int left = 0, right = size - 1;
    while (right > left)
    {
        // Move left pointer to find a negative number
        while (arr1[left] < 0)
            left++;
        // Move right pointer to find a positive number
        while (arr1[right] > 0)
            right--;
        // Swap positive and negative numbers if left < right
        if (left < right)
        {
            changeNumber(arr1, left, right);
        }
    }
}

// Function to rearrange positive and negative numbers alternatively
void rearrangeNumbers(int *arr1, int size) 
{
    int i, j;
    // Split the array into positive and negative parts
    splitPosNeg(arr1, size);

    // Find the first positive number's index
    for (i = 0; arr1[i] < 0; i++);

    // Rearrange the numbers (one positive and one negative alternatively)
    for (j = 1; (j < i) && (arr1[j] < 0); j += 2)
    {
        // Swap positive and negative numbers
        changeNumber(arr1, i, j);
        i++;
    }
    return;
}

int main()
{
    int i, arr1[] = {-4, 8, -5, -6, 5, -9, 7, 1, -21, -11, 19}; 
    int arr_size = sizeof(arr1) / sizeof(arr1[0]);	

    //------------- print original array ------------------	
    printf("The given array is:  \n");
    for (i = 0; i < arr_size; i++)
    {
        printf("%d  ", arr1[i]); // Print the elements of the original array
    }
    printf("\n");
    //----------------------------------------------------------- 

    printf("The rearranged array is:  \n");
    rearrangeNumbers(arr1, 11);
    for (i = 0; i < 11; i++) {
        printf("%d ", arr1[i]); // Print the rearranged array
    }
    return 0;
}

Output:

The given array is:  
-4  8  -5  -6  5  -9  7  1  -21  -11  19  
The rearranged array is:  
-4 7 -5 1 -21 5 -11 8 -9 19 -6

Flowchart:/p>

For more Practice: Solve these Related Problems:

• Write a C program to rearrange an array so that positive and negative numbers alternate, maintaining their original order.
• Write a C program to alternate positive and negative numbers and then append extra numbers at the end.
• Write a C program to rearrange an array with separate partitions for positive and negative numbers using two-pointer technique.
• Write a C program to recursively rearrange an array so that positives and negatives alternate.

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