C - String Library Function

There are several built-in functions available for working with strings. These functions are declared in the <string.h> header file. 

strlen():

Returns the length of a string, excluding the null character.

#include <string.h>
// ...
char str[] = "Hello";
int length = strlen(str);   // length is 5

strcpy():

Copies one string to another.

#include <string.h>
// ...
char source[] = "Hello";
char destination[10];
strcpy(destination, source);   // destination now contains "Hello"

strcat():

Concatenates (appends) one string to the end of another.

#include <string.h>
// ...
char str1[] = "Hello"
char str2[] = " World";
strcat(str1, str2);   // str1 now contains "Hello World"

strcmp():

Compares two strings lexicographically.

#include <string.h>
// ...
char str1[] = "Hello"
char str2[] = "World";
int result = strcmp(str1, str2);   // result is negative (-1)

strchr():

Searches for the first occurrence of a character in a string and returns a pointer to that character.

#include <string.h>
// ...
char str[] = "Hello";
char* ptr = strchr(str, 'l');   // ptr points to the first 'l' in str

strstr():

Searches for the first occurrence of a substring in a string and returns a pointer to that substring.

#include <string.h>
// ...
char str[] = "Hello World";
char* ptr = strstr(str, "World");   // ptr points to the substring "World" in str