C Programming: Replace lowercase characters by uppercase and vice-versa

C String: Exercise-15 with Solution

Write a program in C to read a sentence and replace lowercase characters with uppercase and vice versa.

Sample Solution:

C Code:

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

int main()
{
    char str[100]; // Declare a character array to store the string
    int ctr, ch, i; // Declare variables for counting, characters, and iteration

    printf("\n\nReplace lowercase characters by uppercase and vice-versa :\n"); // Display information about the task
    printf("--------------------------------------------------------------\n");

    printf("Input the string : ");
    fgets(str, sizeof str, stdin); // Read a string from the standard input (keyboard)

    i = strlen(str);
    ctr = i; /* shows the number of chars accepted in a sentence */

    printf("\nThe given sentence is   : %s", str); // Display the original string

    printf("After Case changed the string  is: ");
    for (i = 0; i < ctr; i++) {
        // Check if the character is lowercase, then convert to uppercase, else convert to lowercase
        ch = islower(str[i]) ? toupper(str[i]) : tolower(str[i]);
        putchar(ch); // Output the modified character
    }
    printf("\n\n");
	
	return 0; // Return 0 to indicate successful execution of the program
}

Sample Output:

Replace lowercase characters by uppercase and vice-versa :                                                    
--------------------------------------------------------------                                                
Input the string : This Is A Test String                                                                      
                                                                                                              
The given sentence is   : This Is A Test String                                                               
After Case changed the string  is: tHIS iS a tEST sTRING 

Flowchart :

C Programming Code Editor:

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