NIMCET 2009 — Computer PYQ

To understand how to convert uppercase to lowercase in $ASCII$, we look at the binary patterns of the characters:

1. ASCII Pattern: In the $ASCII$ table, the difference between an uppercase letter and its lowercase counterpart is exactly $32$ in decimal.

   • Example: 'A' is $65$ ($01000001$ in binary).

   • Example: 'a' is $97$ ($01100001$ in binary).

2. The Bit Difference: If you compare the two binary strings, the only difference is at the 6th bit (the bit representing $2^5=32$).

   • Uppercase has a $0$ at the 6th bit.

   • Lowercase has a $1$ at the 6th bit.

3. The Operation: To change a $0$ to a $1$ while keeping all other bits the same, we use the bitwise $OR$ operation with a mask that has a $1$ only at the target position.

   • Mask: $0100000$ (which is $32$ in decimal).

   • Calculation: ${}^{\prime }{A}^{\prime }(01000001)\text{ OR }0100000=01100001{(}^{\prime }{a}^{\prime })$.

Thus, using the mask $0100000$ with the $OR$ operation correctly performs the conversion.