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The strlwr() is string function defined in the string.h header file, which is used to convert all the characters in a String to lower case letters.

Signature of strlwr() function

char * strlwr(char *str);

• str - is a string passed to this method, whose lower case characters needs to be converted to upper case.
• This method changes the character of string passed to it to lower case and returns a char[] array pointer, pointing to this string whose characters are converted to lower case.

Note

The function strlwr() when called on any char[] array, containing a string value, returns its contents as an lower case string.

• Example of strlwr() function




/* Program to convert a String to lower case letters */


#include<string.h>
#include<stdio.h>

int main()
{
char str1[] = "HURRAY! Victory!";
printf("Original String value : %s", str1);
printf("\n");
strupr(str1);
printf("String's upper case value : %s ", str1);

return 0;
}





Output




Original string value : HURRAY! Victory!
String's upper case value : hurray! victory!


A char[] array was initialized with a string value HURRAY! Victory!. When this string was passed to strlwr() function, it changed all the characters in string to lower case letters.




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• Changing the characters in a string to upper case without strupr()


Let's create a program which converts the characters in a string to lower case letters without using strlwr() function.




/* Program to convert a String to lower case letters withut strlwr() function */


#include<string.h>
#include<stdio.h>

int main()
{
char str[] = "Never Give Up!";
printf("Original String is : %s", str);


/* starting index in a char{} array is always zero, 0 */
int i=0;


while(str[i]!='\0')
{
int asc = str[i];
	
	/* When ASCII value of a space is found */
	if(asc==32)
	{
		/* we don't do anything */
	}


	/* When alphabetic characters are found */
	if(asc>=65 && asc<=90)
	{
		asc = asc + 32;
		str[i] = asc;

	}
	
	/* incrementing the index to point to next char value in string */
	i++;
}	


printf("\nString's lower case value : %s", str);

return 0;
}





Output is :




Original String is : Never Give Up!
String's lower case value : never give up!


In the code above, we have changed the cases of characters in a char[] array(which contains a string) to lower case, without using the strlwr() function. To achieve this, we have used the index of each character in a char array to read its ASCII value. When an ASCII value of a character is found to be between 65 and 90, we have added 32 to it, which results in the ASCII value of its lower case equivalent.






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