C Exercises: Calculate the number of 1's in their binary representation and return them as an array

Last update on March 20 2025 12:36:12 (UTC/GMT +8 hours)

14. Count 1's in Binary Array Variants

For a non negative integer in the range 0 ≤ i ≤ n write a C program to calculate the number of 1's in their binary representation and return them as an array.

Example:
Input:
Number: 7
Number of 1's in the binary representation:
0: 0
1: 1
2: 1
3: 2
4: 1
5: 2

Sample Solution:

C Code:

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

// Function to count the number of set bits (1s) in the binary representation of numbers from 0 to 'num'
int* count_Bits(int num, int* returnSize) {
    int *p, i;

    // Allocate memory for the array to store the count of set bits
    p = malloc((num + 1) * sizeof(int));
    *returnSize = num + 1; // Set the return size to 'num + 1'

    p[0] = 0; // The count of set bits in 0 is 0
    for (i = 1; i <= num; i++) {
        // Use bitwise manipulation to count the set bits for each number
        // Count the number of set bits by using the formula: p[i] = p[i & (i - 1)] + 1
        p[i] = p[i & (i - 1)] + 1;
    }

    return p; // Return the array containing the count of set bits for numbers from 0 to 'num'
}

// Main function to test the count_Bits function and display the count of set bits for numbers up to 'num'
int main(void) {
    int *p;
    int returnSize;
    int i = 7;
    printf("Number: %d", i);
    printf("\nNumber of 1's in the binary representation:\n");

    // Calculate and display the count of set bits for numbers up to 5
    p = count_Bits(5, &returnSize);
    for (i = 0; i < returnSize; i++) {
        printf("%X:\t%d\n", i,  p[i]);
    }

    free(p); // Free the dynamically allocated memory
    return 0;
}

Sample Output:

Number: 7
Number of 1's in the binary representation:
0:	0
1:	1
2:	1
3:	2
4:	1
5:	2

Flowchart:

For more Practice: Solve these Related Problems:

• Write a C program to create an array where each element is the count of 1's in the binary representation of numbers 0 to n.
• Write a C program to compute the binary ones count for each integer using bit manipulation techniques.
• Write a C program to calculate the number of 1's in binary representation recursively and store the results in an array.
• Write a C program to optimize the counting of 1's using dynamic programming for numbers 0 to n.

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