set_ith_bit.cpp

#include <bits/stdc++.h>

using namespace std;

int setIthBit(int num, int i) {
    int mask = (1 << i);
    return (mask | num);
}

int main() {
    int n, i;
    cin >> n >> i;
    cout << setIthBit(n, i) << '\n';
    return 0;
}

/*
───────────────────────────────────────────────────────────────────────────────────
    Bit Numbering Convention (Important) 
───────────────────────────────────────────────────────────────────────────────────
    Bits are counted from **right to left**
    The **Least Significant Bit (LSB)** — the rightmost bit — is position **0**
    The **Most Significant Bit (MSB)** is the leftmost bit
    Example:
        Binary:   1  0  0  1
        Position: 3  2  1  0
                  ↑        ↑
                 MSB      LSB
    i = 0 → refers to the rightmost bit
    i = 3 → refers to the leftmost bit (in 4-bit example)
───────────────────────────────────────────────────────────────────────────────────
    Example Run
───────────────────────────────────────────────────────────────────────────────────
    Input:
    9 1
    Binary of 9 = 1001
                    ↑
             set this bit (i = 1)
    mask is shorthand for bitmask and i = position
    mask = (1 << 1)
         = 2
         = (00000010)
    num | mask = (00001001) | (00000010)
               = (00001011)
    After setting → 00001011 = 11
    Output:
    11
───────────────────────────────────────────────────────────────────────────────────
*/