diff --git a/ex04/ft_str_is_lowercase.c b/ex04/ft_str_is_lowercase.c
new file mode 100644
index 0000000..e5478b9
--- /dev/null
+++ b/ex04/ft_str_is_lowercase.c
@@ -0,0 +1,34 @@
+/* ************************************************************************** */
+/*                                                                            */
+/*                                                        :::      ::::::::   */
+/*   ft_str_is_lowercase.c                              :+:      :+:    :+:   */
+/*                                                    +:+ +:+         +:+     */
+/*   By: tischmid <marvin@42.fr>                    +#+  +:+       +#+        */
+/*                                                +#+#+#+#+#+   +#+           */
+/*   Created: 2023/03/19 11:03:56 by tischmid          #+#    #+#             */
+/*   Updated: 2023/03/19 11:12:03 by tischmid         ###   ########.fr       */
+/*                                                                            */
+/* ************************************************************************** */
+
+int	ft_str_is_lowercase(char *str)
+{
+	int	i;
+
+	i = 0;
+	while(str[i] >= 'a' && str[i] <= 'z')
+	{
+		++i;
+	}
+	return (str[i] == '\0');
+}
+
+/* ////
+#include <stdio.h>
+
+int	main(void)
+{
+	char	s[] = "abcdef";
+	printf("%d\n", ft_str_is_lowercase(s));
+	return (0);
+}
+*/ ////