C Standard Library
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C <ctype.h> - islower() Function

The C <ctype.h> islower() function is used to check if the given character is a lowercase letter. In the default "C" locale, the following are the lowercase letters: abcdefghijklmnopqrstuvwxyz. Other locales may consider a different selection of characters as lowercase characters.


int islower ( int ch );               


ch Specify the character to be checked, casted to an int, or EOF.

Return Value

Returns non-zero value (i.e, true) if ch is a lowercase letter, else returns zero (i.e, false).


The example below shows the usage of islower() function.

#include <stdio.h>
#include <ctype.h>
int main (){
  char str[50] = "99HEllo";

  //counting the number of lowercase
  //characters in str
  int i = 0, count = 0;
  while(str[i]) {

  //displaying the output
  printf("%s contains %d lowercase letters.", str, count);
  return 0;

The output of the above code will be:

99HEllo contains 3 lowercase letters.

❮ C <ctype.h> Library