Here, we will read an uppercase character from the user and convert it into lowercase.

Program:

The source code to covert an uppercase character into lowercase without using the library function is given below. The given program is compiled and executed using GCC compile on UBUNTU 18.04 OS successfully.

// C program to covert an uppercase character into lowercase
// without using library function

#include <stdio.h>

char toLowerCase(char ch)
{
    ch = ch + 32;
    return ch;
}

int main()
{
    char ch;

    printf("Enter a uppercase character: ");
    scanf("%c", &ch);

    printf("Lowercase character is: %c\n", toLowerCase(ch));

    return 0;
}

Output:

Enter a uppercase character: Q
Lowercase character is: q

Explanation:

Here, we created two functions toLowerCase() and main(). The toLowerCase() function is used to covert the uppercase character to the lowercase character.

In the main() function, we read an uppercase character from the user and converted the entered character into lowercase using the toLowerCase() function.