16. Built in Functions

Built in Functions

C provides us some built in functions to help us, write c programs quickly and easily.

Where do these functions exists ?

  1. These functions exists in library files provided by c.
  2. Header files contain information about function prototype.

String related functions are used to manipulate strings, calculate length and perform different operations on string.

#include<string.h>
int main() {
  char name[50] = "Jayant Malik";

  // length of string.
  // navigates till null character and returns the count.
  printf("Length : %d\n", strlen(name));

  // compare two strings
  // navigates till last index and returns difference of,
  // ascii values of characters present,
  // at index.
  printf("Is Has equals has : %d\n", strcmp("Has", "has"));
  printf("Is Has equals java : %d\n", strcmp("Has", "java"));

  // compare n characters of string.
  printf("Is Jayant compares with Jayant Malik : %d\n", strncmp("Jayant", "Jayant Malik", 6))

  // copy one string to another string.
  // this function overwrites the string.
  strcpy("Snake Lion", name);
  printf("Name after copy : %s\n", name);

  // Concatenation of string
  // this function appends name after string.
  strcat(name, "Snake Lion");
  printf("Name after concatenation : %s\n", name);

  return 0;
}

#include<math.h>
int main() {
  int number = 20;

  // math related functions
  printf("Sin %d : %f\n", number, sin(number));
  printf("Cos %d : %f\n", number, cos(number));
  printf("Tan %d : %f\n", number, tan(number));
  printf("Cosec %d : %f\n", number, 1 / sin(number));
  printf("Sec %d : %f\n", number, 1 / cos(number));
  printf("Cot %d : %f\n", number, 1 / tan(number));

  // Modulus of floating point numbers.
  // on linux use : gcc filename -lm
  // to link libm library that contains
  // math decimal point related functions.
  printf("20.5 % 3.6 = %f\n", fmod(20.5, 3.6));

  return 0;
}

    char *strcpy (char *dest, char *src);
    //Copy src string into dest string.

    char *strncpy(char *string1, char *string2, int n);
    //Copy first n characters of string2 to stringl .

    int strcmp(char *string1, char *string2);
    //Compare string1 and string2 to determine alphabetic order.

    int strncmp(char *string1, char *string2, int n);
    //Compare first n characters of two strings.

    int strlen(char *string);
    //Determine the length of a string.

    char *strcat(char *dest, const char *src);
    //Concatenate string src to the string dest.

    char *strncat(char *dest, const char *src, int n);
    //Concatenate n chracters from string src to the string dest.

    char *strchr(char *string, int c);
    //Find first occurrence of character c in string.

    char *strrchr(char *string, int c);
    //Find last occurrence of character c in string.

    char *strstr(char *string2, char string*1);
    //Find first occurrence of string string1 in string2.

    char *strtok(char *s, const char *delim) ;
    //Parse the string s into tokens using delim as delimiter.



    void *calloc(int num elems, int elem_size);
    //Allocate an array and initialise all elements to zero .

    void free(void *mem address);
    //Free a block of memory.

    void *malloc(int num bytes);
    //Allocate a block of memory.

    void *realloc(void *mem address, int newsize);
    //Reallocate (adjust size) a block of memory.



    void* memcpy(void* s, const void* ct, int n);
    //Copies n characters from ct to s and returns s. s may be corrupted if objects overlap.

    int memcmp(const void* cs, const void* ct, int n);
    //Compares at most (the first) n characters of cs and ct, returning negative value if cs<ct, zero if cs==ct, positive value if cs>ct.

    void* memchr(const void* cs, int c, int n);
    //Returns pointer to first occurrence of c in first n characters of cs, or NULL if not found.

    void* memset(void* s, int c, int n);
    //Replaces each of the first n characters of s by c and returns s.

    void* memmove(void* s, const void* ct, int n);
    //Copies n characters from ct to s and returns s. s will not be corrupted if objects overlap.




    int isalnum(int c);
    //The function returns nonzero if c is alphanumeric

    int isalpha(int c);
    //The function returns nonzero if c is alphabetic only

    int iscntrl(int c);
    //The function returns nonzero if c is a control chracter

    int isdigit(int c);
    //The function returns nonzero if c is a numeric digit

    int isgraph(int c);
    //The function returns nonzero if c is any character for which either isalnum or ispunct returns nonzero.

    int islower(int c);
    //The function returns nonzero if c is a lower case character.

    int isprint(int c);
    //The function returns nonzero if c is space or a character for which isgraph returns nonzero.

    int ispunct(int c);
    //The function returns nonzero if c is punctuation

    int isspace(int c);
    //The function returns nonzero if c is space character

    int isupper(int c);
    //The function returns nonzero if c is upper case character

    int isxdigit(int c);
    //The function returns nonzero if c is hexa digit

    int tolower(int c);
    //The function returns the corresponding lowercase letter if one exists and if isupper(c); otherwise, it returns c.

    int toupper(int c);
    //The function returns the corresponding uppercase letter if one exists and if islower(c); otherwise, it returns c.



    void perror(const char *s);
    //produces a message on standard error output describing the last error encountered.

    char *strerror(int errnum );
    //returns a string describing the error code passed in the argument errnum.