C Programming: Convert a string to lowercase

Last update on August 06 2025 13:03:22 (UTC/GMT +8 hours)

22. Convert String to Lowercase

Write a program in C to convert a string to lowercase.

Sample Solution:

C Code:

#include<stdio.h>
#include<ctype.h>

int main() {
    int ctr = 0; // Variable to keep track of position in the string
    char str_char; // Variable to store each character of the string
    char str[100]; // Array to store the input string

    printf("\n Convert a string to lowercase :\n");
    printf("----------------------------------");
    printf("\n Input a string in UPPERCASE : ");
    fgets(str, sizeof str, stdin); // Read a string including spaces from the user

    printf(" Here is the above string in lowercase :\n ");

    while (str[ctr]) { // Loop through each character of the string until the null character is encountered
        str_char = str[ctr]; // Retrieve each character from the string
        putchar(tolower(str_char)); // Convert the character to lowercase using tolower() function and print it
        ctr++; // Move to the next character in the string
    }

    return 0; // Return 0 to indicate successful execution of the program
}

Output:

 Convert a string to lowercase :
----------------------------------
 Input a string in UPPERCASE : THE QUICK BROWN FOX JUMPS OVER THE LAZY DOG.
 Here is the above string in lowercase :
 the quick brown fox jumps over the lazy dog.

Flowchart:

Flowchart: Convert a string to lowercase

For more Practice: Solve these Related Problems:

Write a C program to convert a given string to lowercase manually without using library functions.
Write a C program to convert all uppercase letters to lowercase using ASCII arithmetic operations.
Write a C program to transform a string to lowercase and then reverse its characters.
Write a C program to convert a sentence to lowercase and count the frequency of vowels afterward.

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C Programming Code Editor:

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