C language to determine the English character case

C language isupper() function: determine whether the character is uppercase or not
The header file:

 #include <ctype.h>

Definition function:

int isupper(int c);

Check whether the parameter c is capitalized.

Return value: returns non-0 if parameter c is uppercase; otherwise returns 0.

Note: this is a macro definition, not a real function.

Example: find an uppercase character in the string STR.

#include <ctype.h>
main(){
  char str[] = "123c@#FDsP[e?";
  int i;
  for(i = 0; str[i] != 0; i++)
    if(isupper(str[i]))
      printf("%c is an uppercase charactern", str[i]);
}

Execution results:

F is an uppercase character
D is an uppercase character
P is an uppercase character

C islower() function: determines whether a character is lowercase
The header file:

#include <ctype.h>

Islower () is used to determine whether a character is lowercase. The prototype is:

  int islower(int c);

[parameter] c is the character to be detected.

[return value] if the parameter c is lowercase, a non-zero value is returned; otherwise, 0 is returned.

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

Example: determines which lowercase letters are in the STR string.

#include <ctype.h>
main(){
  char str[] = "123@#FDsP[e?";
  int i;
  for(i = 0; str[i] != 0; i++)
    if(islower(str[i]))
      printf("%c is a lower-case charactern", str[i]);
}

Output results:

c is a lower-case character
s is a lower-case character
e is a lower-case character