C islower() function

C islower(int ch)

The islower() function is used to check whether a character is lowercase alphabet (a-z) or not. The function is defined in the ctype.h header file.

Note: Letter case is the distinction between the letters that are in larger uppercase or capitals (or more formally majuscule) and smaller lowercase (or more formally minuscule) in the written representation of certain languages.


int islower( int arg );

islower() Parameters:

Name Description Required /Optional
ch ch is a character of class lower in the current locale. Required

Return value from islower()

  • The islower() function returns non-zero if ch is a lowercase letter; otherwise, returns 0.

Example: C islower() function

#include <stdio.h>
#include <ctype.h>
int main()
    char ch;
    ch = 'y';
    printf("\nIf %c is lower character or not? %d", ch, islower(ch));
    ch = 'Y';
    printf("\nIf %c is lower character or not? %d", ch, islower(ch));
    ch = 'A';
    printf("\nIf %c is lower character or not? %d", ch, islower(ch));


If y is lower character or not? 2
If Y is lower character or not? 0
If A is lower character or not? 0

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C Programming: Tips of the Day

Reading a string with scanf :

An array "decays" into a pointer to its first element, so scanf("%s", string) is equivalent to scanf("%s", &string[0]). On the other hand, scanf("%s", &string) passes a pointer-to-char[256], but it points to the same place.

Then scanf, when processing the tail of its argument list, will try to pull out a char *. That's the Right Thing when you've passed in string or &string[0], but when you've passed in &string you're depending on something that the language standard doesn't guarantee, namely that the pointers &string and &string[0] -- pointers to objects of different types and sizes that start at the same place -- are represented the same way.

Ref : https://bit.ly/3pdEk6f