tolower() Function in C

tolower() function in C is used to convert the uppercase alphabet to the lowercase alphabet. It does not affect characters other than uppercase characters. It is defined in the <ctype.h> header file in C.

Syntax

The syntax of tolower() function is:

int tolower(int c);

Parameter

• This function takes a character as a parameter.

Return Value

• It returns the ASCII value corresponding to the lowercase of the character passed as the argument.

Examples of tolower() Function

Example 1

The below C program demonstrates the tolower() function.

C

// C program to demonstrate
// example of tolower() function.
#include <ctype.h>
#include <stdio.h>

int main()
{

    // convert 'M' to lowercase
    char ch = tolower('M');

    // Printing the lowercase letter
    printf("%c", ch);

    return 0;
}

Output

m

Example 2

The below code converts all uppercase letters in the string to their lowercase equivalents, while leaving other characters unchanged.

C

// C program to demonstrate
// example of tolower() function.
#include <ctype.h>
#include <stdio.h>

int main()
{

    char s[] = "Code_in_C_@0123";

    // This will just convert
    // uppercase letters in string
    // to lowercase. Other characters
    // will remain unaffected.
    for (int i = 0; i < strlen(s); i++) {
        s[i] = tolower(s[i]);
    }

    // Printing the output
    printf("%s", s);

    return 0;
}

Output

code_in_c_@0123