This program reads a sentence and swaps the case of every letter — uppercase becomes lowercase, lowercase becomes uppercase. Digits, spaces, and punctuation are left unchanged. The <ctype.h> functions isupper(), islower(), toupper(), and tolower() make this clean and portable across all ASCII and extended character sets. The original post used conio.h, void main(), a broken …
A palindrome is a word, sentence, or sequence that reads the same forward and backward — ignoring differences in capitalization for word-level palindromes. Examples: “racecar”, “GADAG”, “level”, “9009”. The most efficient check uses a two-pointer approach: one pointer starts at the left end, one at the right, and they advance toward each other until they …
String concatenation in C joins two strings end-to-end into a single result. The standard library provides strcat() for this, but writing it manually teaches how C strings work: they are null-terminated char arrays, and concatenation means walking to the end of the destination string then copying source characters one by one until the null terminator. …