Common C language standard library functions

1. mathematical functions

ABS (X)

Cos (X)

FABS (X)

Ceil (x) // calculates the maximum integer not less than X

Floor (x) // returns the smallest integer not greater than X.

Log (x) // calculate the natural logarithm of X

Log10 (x) // calculates the logarithm of X (as low as 10)

Pow (x, y)

Sin (X)

SQRT (X)

2. Character Processing functions

Int isdigit (int c)

Int isalpha (int c)

Int isalnum (INT c) // determines whether C is a number or letter.

Int islower (int c)

Int isupper (int c)

Int toupper (int c)

Int tolower (int c)

3. String

Char * strchr (char * s, int c) // whether the character C is contained

Char * strstr (char * S1, char * S2) // whether S1 contains string S2

Char * strlwr (char * s) // converts all letters in S to lowercase letters.

Char * strupr (char * s) // converts all letters in S into uppercase letters.

Char * strcpy (char * S1, char * S2)

Char * strncpy (char * S1, char * S2, int N)

Char * strcat (char * S1, char * S2)

Int strcmp (char * S1, char * 2)

Int stricmp (char * S1, char * S2)

Int strlen (const char * string)

Char * strncat (char * strdestination, const char * strsource, size_t count)

Int strncmp (const char * string1, const char * string2, size_t count)

Char * strrev (char * string)

Void * memcpy (void * S1, void * S2, int N)

Void * memset (void * s, int C, int N)

4. String Conversion Functions

Int atoi (char * s) // the content of the character is converted into a decimal integer

Float atof (char * s) // the content of the string is converted into a decimal floating point number.

Char * ITOA (INT value, char * string, int Radix) // write the integer value to the string in Radix notation.