8.1 String Basics and the Null Terminator
C has no dedicated string type — a string is simply a char array ending with the special null character ' ', which marks where the text stops. "Hello" therefore actually occupies 6 bytes (5 letters + the terminator), not 5. Every string-handling function relies on finding this to know where to stop reading or writing.
char str[6] = "Hello";C strings are char arrays terminated by a NULL character ( ).
Functions like strlen() scan until they hit to find the length.
Two-Pointer Palindrome Verification in C
Because a C string is a null-terminated character array, we can verify whether it is a palindrome using two pointers moving inward, achieving O(n) time and O(1) space:
int isPalindrome(char *s) {
int i = 0, j = strlen(s) - 1;
while (i < j) {
if (s[i] != s[j]) return 0; // false
i++;
j--;
}
return 1; // true
}8.2 Standard String-Handling Functions
The library provides the core toolkit for text manipulation. These functions all scan up to the null terminator internally, so passing a char array without one causes undefined (often crashing) behaviour.
| Function | Purpose |
|---|---|
strlen(s) | Returns the length of s, not counting |
strcpy(dst,src) | Copies src into dst, including |
strcat(dst,src) | Appends src onto the end of dst |
strcmp(a,b) | Returns 0 if equal; <0 or >0 otherwise |
strchr(s,c) | Finds first occurrence of character c in s |
