luc105.c

Problem Statement

luc105.c

Write a function checkbits(x, p, n) which returns true if all 'n' bits starting from position 'p' are turned on.

Source Code

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

int checkbits(unsigned int x, int p, int n);

int main()
{
    unsigned int x;
    int p, n;

    printf("Enter number (x): ");
    scanf("%u", &x);
    printf("Enter starting position (p) and count (n): ");
    scanf("%d %d", &p, &n);

    if (checkbits(x, p, n))
        printf("TRUE: %d bits starting at %d are ON.\n", n, p);
    else
        printf("FALSE: Not all specified bits are ON.\n");

    return 0;
}

int checkbits(unsigned int x, int p, int n)
{
    unsigned int mask;
    
    // Create a mask of n 1s. E.g., if n=3, mask=000...0111
    mask = (1 << n) - 1;
    
    // Shift mask to position p
    mask = mask << p;

    // Check if bits in x match the mask
    return (x & mask) == mask;
}

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● Author - Amit Dutta · Updated - 08 Feb 2026