A simple method for case-and-write conversion of letters in C language _c language

C language ToLower () function: Convert uppercase letters to lowercase letters
header file:

#include <ctype.h>

To define a function:

int toupper (int c);

Function Description: If the parameter c is a lowercase letter, the corresponding uppercase letter is returned.

Return value: Returns the converted uppercase letter, returning the parameter C value if no conversion is required.

Example: Converts lowercase letters within the s string to uppercase letters.

#include <ctype.h>
Main () {
 char s[] = "abcdefgh12345;! #$";
 int i;
 printf ("Before ToUpper ():%s\n", s);
 for (i = 0; i < sizeof (s); i++)
  s[i] = ToUpper (s[i));
 printf ("After ToUpper ():%s\n", s);
}

Execution results:

Before ToUpper (): abcdefgh12345;! #$ after
toupper (): abcdefgh12345;! #$

C language ToLower () function: Convert uppercase letters to lowercase letters
header file:

#include <stdlib.h>

To define a function:

int tolower (int c);

Function Description: If the parameter C is uppercase, the corresponding lowercase letter is returned.

Return value: Returns the converted lowercase letter, returning the parameter C value if no conversion is required.

Example: Converts uppercase letters within the s string to lowercase letters.

#include <ctype.h>
Main () {
 char s[] = "abcdefgh12345;! #$";
 int i;
 printf ("Before ToLower ():%s\n", s);
 for (i = 0; i < sizeof (s); i++)
  s[i] = ToLower (s[i));
 printf ("After ToLower ():%s\n", s);
}

Execution results:

Before ToLower (): abcdefgh12345;! #$ after
tolower (): abcdefgh12345;! #$