Summary of common functions of C language (non-original)

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The mathematical library functions are declared in MATH.H, mainly:
ABS (x) to find the absolute value of the integer number x
Cosine of cos (x) x (radians)
Fabs (x) to find the absolute value of the floating-point number X
Ceil (x) to find the smallest integer not less than X
Floor (x) to find the smallest integer not greater than X
Log (x) to find the natural logarithm of x E
LOG10 (x) to find the logarithm of X (base 10)
The POW (x, y) asks X's Y-square
Sin (x) to find the sine of x (radians)
sqrt (x) to find the square root of X
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Character processing functions
It is stated in Ctype.h that the main:
int isdigit (int c) to determine if C is a numeric character
int isalpha (int c) to determine if C is a letter
int isalnum (int c) determines whether C is a number or a letter
int islower (int c) to determine if C is a lowercase letter
int isupper (int c) to determine if C is an uppercase letter
int toupper (int c) If c is a lowercase letter, return its uppercase letter
int tolower (int c) If C is an uppercase letter, returns its lowercase letter

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string and memory manipulation functions are declared in string.h, which are commonly used:

char * STRCHR (char * s, int c), if s contains the character C, returns a pointer to the character that the first occurrence of s, otherwise returns null
char * STRSTR (char * s1, char * s2), if S2 is a substring of S1, returns a pointer to S1 where S2 first appears, otherwise returns null
char * STRLWR (char * s) turns the letters in s to lowercase
char * STRUPR (char * s) turns the letters in S to uppercase
char * strcpy (char * s1, char * s2) copies the contents of the string S2 to S1
char * strncpy (char * s1, char * s2,int N) copies the contents of the string S2 to S1, but copies up to n bytes.
If the number of copied bytes reaches N, then the end of ' s1 ' will not be written to the
char * strcat (char * s1, char * s2) adds a string S2 to the end of S1
The int strcmp (char * s1, char * s2) compares two strings, which are case-sensitive. If the return value is less than 0, the S1 is preceded by S2 in dictionary order;
The return value equals 0, which means that two strings are the same; the return value is greater than 0, then the S1 is in dictionary order after S2.
The int stricmp (char * s1, char * s2) compares two strings, regardless of the casing. Other and strcmp with.
void * memcpy (void * s1, void * s2, int n) copies the n-byte content at the S2 of the memory address to the memory address S1.
void * memset (void * s, int c, int n) Place all n bytes starting with the memory address S as C.
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A function such as converting a string to an integer, or converting an integer to a string. They are defined in the Stdlib.h:

int atoi (char *s) converts the contents of the string s into an integer number returned. For example, if the contents of the string s are "1234", then the function return value is 1234.
Double atof (char *s) converts the contents of the string s into floating-point numbers. A to int.////a to Flor
char *itoa (int value, char *string, int radix), and integer value value is written to string as a radix-binary notation. Like what:
Char szvalue[20];
Itoa (32,szvalue,10) makes the content of Szvalue become "32";
Itoa (32,szvalue,16) makes the szvalue content "20"

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Summary of common functions of C language (non-original)