The standard C library offers a number of functions that allow users to modify character values. The tolower function is one of such functions, which we are going to
discuss here. In this article, you can expect to:
Return: unmodified integer value of parameter c or a sum of received parameter and 32 (c + 32).
Parameter list: (int
c) - an integer value to be modified, if it represents an uppercase character.
Header file:<ctype.h>.
1. So, what is tolower function?
The tolower function in C programming language modifies
uppercase characters to lowercase ones. The uppercase characters in C programming language fall in the
ASCII range from 65 to
90. To these values does the tolower function add 32. Which
turns a character from uppercase to lowercase.
If you were to pass any other non-uppercase character to the tolower function, you would receive the exact same value back
from this function. To see how to use this ctype.h library
function, you can consider the code snippet below (example 1).
Example 1: Printing lowercase alphabet using tolower function.
#include <stdio.h>
#include <ctype.h>
intmain()
{
printf("Now you know the ");
for(inti = 'A'; i <= 'Z'; i++)
{
printf("%c", tolower(i));
}
return0;
}
Possible output:
Now you know the abcdefghijklmnopqrstuvwxyz
2. And how to implement the tolower function in C?
Now, for an accurate implementation of the tolower function,
you should make sure that your function returns appropriate values. If the received parameter is not an
uppercase character, you should return the same integer value. Otherwise, you should add 32 to the
received parameter and return the sum. Below you can find a way to write this in C programming language
(example 2).
Example 2: Rewritten tolower function in C.
intour_tolower ( int c)
{
if(c >= 'A' && c <= 'Z' )
return(c + 32);
return(c);
}
Here, we define the our_tolower function that receives and
returns integer values. The return value depends on the condition (on line 3). Given that this
condition is true, it means that the received parameter can be implicitly (or explicitly) converted to
an uppercase character. In which case, 32 is added (on line 4) and the sum is returned. If the
condition is false, however, then the parameter value is equal to the return value.
3. Quiz of the tolower function
Quiz : Rewritten tolower function in C
1What
does the tolower function NOT do?
2Which of the following ranges contain all the lowercase alphabet
characters?
