Strings

Characters

Characters are assigned by an integer on an ASCII table. This means we can do arithmetic on characters.

char myChar = 'a';
myChar += ('z' - 'x'); // 'z' - 'x' = 2, and 'a' + x = 'c'

Strings

A string is just a char array in C

The following are equivalent:

char s[] = "Hello";
char t[] = {'H', 'e', 'l', 'l', 'o', '\0'}; // Null char required

We can have Pointers to strings

char s[] = "Hello";
char *t = "Hello"; // This becomes an immutable constant

printf("%s\n", t); // Output "Hello"
printf("%zu\n", sizeof(s)); // Ouptut 6 (because + null char)
printf("%zu\n", sizeof(t)); // Ouptup 8 (because pointer)

String Utils

/**
 * @returns the lengnth of s. Does not include null char
 */
size_t strlen(const char *s);

/**
 * Copies s1 into s0
 * s0 must have enough room including the null character, or this may overwrite
 * bits we do not want it to touch
 * 
 * @returns pointer to `s0`
 */
char *strcpy(char *s0, const char *s1);

=REMEMBER TO INCLUDE SPACE FOR NULL CHAR=

/**
 * Copies the first `n` elements from s1 into s0.
 * Will not add null character for you, DIY
 * 
 * @returns pointer to `s0`
 */
char *strncpy(char *s0, const char *s1, size_t n);

/**
 * Concatnates s1 onto s0.
 * s0 must have enough room.
 * A null character is added to the end automatically[w]()
 * 
 * @returns pointer to `s0`
 */
char *strcat(char *s0, const char *s1);

/**
 * Concatnates the first n characters of s1 onto s0.
 * s0 must have enough room.
 * A null character is added to the end automatically[]()
 * 
 * @returns pointer to `s0`
 */
char *strncat(char *s0, const char *s1, size_t n);

/**
 * Compares the two strings lexicographically (ie. comparing ASCII values)
 * 
 * @returns < 0 if s0 < s1
 * @returns > 0 if s0 > s1
 * @returns 0 if s0 == 1
 * @returns the index where the characters first differ
 */
int strcmp(const char *s0, const char *s1);

#include <stdio.h>

#include <string.h>

  

int main() {

char s[20] = "Led ";

char t[10] = {0}; // IMPORTANT: INITIALIZE or there will be strange behaviour

  

strncpy(t, "Zeppole", 4);

strncat(t, "eline", 4);

strcat(s, t);

  

printf("%lu\n%s\n%s\n", strlen(s), s, t);

  

return 0;

}