The method of using C language to judge the case of English characters _c language

C language Isupper () function: To determine whether the character is uppercase English letters
header file:

 #include <ctype.h>

To define a function:

int isupper (int c);

Function Description: Check whether the parameter C is an uppercase English letter.

Return value: If parameter C is an uppercase English letter, returns a non 0, otherwise returns 0.

Additional description: This is a macro definition, not a true function.

Example: Find characters in the string str that are uppercase English letters.

#include <ctype.h>
Main () {
  char str[] = "123c@ #FDsP [E?";
  int i;
  for (i = 0; Str[i]!= 0; i++)
    if (Isupper (str[i)))
      printf ("%c be an uppercase character\n", str[i));

Execution results:

F is a uppercase character
D is a uppercase character
P is a uppercase character

C language Islower () function: To determine whether a character is a lowercase letter
header file:

#include <ctype.h>

Islower () is used to determine whether a character is a lowercase letter, and its prototype is:

  int islower (int c);

"Parameter" C is the character you want to detect.

return value if parameter C is a lowercase English letter, returns a value other than 0, otherwise returns 0.

Note that this is a macro definition, not a true function.

"Instance" determines which of the STR strings are lowercase letters.

#include <ctype.h>
Main () {
  char str[] = "123@ #FDsP [E?";
  int i;
  for (i = 0; Str[i]!= 0; i++)
    if (Islower (str[i)))
      printf ("%c be a lower-case character\n", Str[i]);

Output results:

C is a lower-case character
S. A lower-case character
E is a lower-case character