C PROGRAMMING PROGRAM • STRINGS

Toggle the Case of Every Alphabet

Learn how to toggle the case of every alphabet using a clear C program.

Beginnerisupper()tolower()toupper()

PROBLEM UNDERSTANDING

Input and expected output

Sample input

CodeBHAVYA 2026

Sample output

Toggled: cODEbhavya 2026

COMPLETE C PROGRAM

Complete C implementation

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

int main(void)
{
    char text[300];

    fgets(text, sizeof text, stdin);
    for (int index = 0; text[index] != '\0'; index++) {
        unsigned char value = (unsigned char) text[index];
        if (isupper(value)) text[index] = (char) tolower(value);
        else if (islower(value)) text[index] = (char) toupper(value);
    }
    printf("Toggled: %s", text);
    return 0;
}

CURRENT STEP

Select Start to walk through the important lines.

SELECTED LINE

No line selected

EXPECTED OUTPUT FOR THE SAMPLE

Toggled: cODEbhavya 2026

0%Step 0 of 0

PROGRAM EXPLANATION

Algorithm and explanation

Read the required input values.
Convert uppercase letters to lowercase and lowercase letters to uppercase.
Display the computed result.

Convert uppercase letters to lowercase and lowercase letters to uppercase.

EFFICIENCY

Time and space complexity

Time complexity

O(n)

Auxiliary space

O(1)

DEBUGGING CHECKLIST

Common mistakes

Check this

Use the correct format specifier for every variable.

Check this

Initialize variables before using their values.

Check this

Check braces, semicolons and input order carefully.

Try it yourself

Practice: Run the program with the sample input, predict its output, and then test one boundary case of your own.