Program 60 - CSU1128 - CSE 2026 - Shoolini University

Program to convert a sentence entered by the user to lowercase by using the external library ctype.h

Explanation

The program converts a sentence entered by the user to lowercase using the ctype.h library function tolower.

Header

The code begins with including the standard input-output header file and the ctype header file using #include <stdio.h> and #include <ctype.h>.

Variable Declaration

The main() function is defined, and a character array is declared:

char sentence[100];: Array to hold the input sentence with a maximum length of 99 characters plus the null terminator.

Program Description

The program prints a description message for the user to understand its functionality.

User Input

The user is prompted to enter a sentence:

printf("Enter a sentence: ");: Prompts the user to enter a sentence.
fgets(sentence, sizeof(sentence), stdin);: Reads the sentence including spaces and stores it in the array sentence.

Convert to Lowercase

The program converts the sentence to lowercase using the tolower function:

for (int i = 0; sentence[i] != '\0'; i++): Loops through each character of the sentence until the null terminator is reached.
sentence[i] = tolower(sentence[i]);: Converts each character to lowercase using the tolower function.

Output Result

The program prints the converted sentence:

printf("Lowercase: %s\n", sentence);: Prints the sentence after converting it to lowercase.

Program End

The program ends with return 0; to indicate successful execution.

Code

                    
/*
 * -----------------------------------------------------------
 * Logic Building with Computer Programming (CSU1128)
 * Instructor: Dr. Pankaj Vaidya | Author: Divya Mohan
 * 
 * This code is a part of the educational initiative by dmj.one
 * with aim of empowering and inspiring learners in the field of
 * Computer Science and Engineering through the respective courses.
 * 
 * (c) 2022, Divya Mohan for dmj.one. All rights reserved.
 * -----------------------------------------------------------
 */

#include <stdio.h>
#include <ctype.h>
int main()
{
    printf("\n\n Program to convert a sentence entered by the user to lowercase by using the external library ctype.h \n\n");

    char sentence[100];

    printf("Enter a sentence: ");
    fgets(sentence, sizeof(sentence), stdin);

    // Convert the sentence to lowercase
    for (int i = 0; sentence[i] != '\0'; i++)
    {
        sentence[i] = tolower(sentence[i]);
    }

    printf("Lowercase: %s\n", sentence);

    return 0;
}

Output

Program to convert a sentence entered by the user to lowercase by using the external library ctype.h

Enter a sentence: This IS a DeMo sentence.
lowercase: this is a demo sentence