Change case of each character in a string

Problem Statement: Write a program to change the case (lower to upper and upper to lower cases) of each character of a given string.

Examples:

Example 1:
Input: String str = “javA”
Output: JAVa
Explanation:
 Changed the lower case characters to uppercase and vice versa.

Example 2:
Input: String str = “take u forward IS Awesome”
Output: TAKE U FORWARD is aWESOME
Explanation: Changed the lower case characters to uppercase and vice versa.

Solution

Disclaimer: Don’t jump directly to the solution, try it out yourself first.

Solution 1:

Approach:

Keep on iterating the given string:
If the corresponding character is uppercase then convert it to lowercase using ascii value by adding 32 to its current ascii value and then typecasting it.
Else if the character is lowercase then convert it to uppercase using ascii value by subtracting 32 from its current ascii value and then typecasting it.
If any whitespace then keep it as it is.

Return the final string

Code:

C++ Code

#include<bits/stdc++.h>

using namespace std;
void solve(string str, int n) {

  for (int i = 0; i < n; i++) {
    int ascii = (int) str[i]; // calculating ascii value

    if (ascii >= 65 && ascii <= 90) // if uppercase
      str[i] = ((char)(ascii + 32));

    else if (ascii >= 97 && ascii <= 122) // if lowercase
      str[i] = ((char)(ascii - 32));

  }

  cout << "Resultant string: " << "\n";
  cout << str << "\n";
}
int main() {
  // Input string
  string str = "take u forward IS Awesome";
  int n = str.length();

  solve(str, n);
  return 0;
}

Output:

Resultant string:
TAKE U FORWARD is aWESOME

Time Complexity: O(n)

Space Complexity: O(1)

Java Code

public class tUf {
  public static String solve(String str, int n) {
    StringBuffer ans = new StringBuffer();
    for (int i = 0; i < n; i++) {
      int ascii = (int) str.charAt(i);

      if (ascii >= 65 && ascii <= 90)
        ans.append((char)(ascii + 32));

      else if (ascii >= 97 && ascii <= 122)
        ans.append((char)(ascii - 32));

      else if (str.charAt(i) == ' ')
        ans.append(' ');
    }

    return ans.toString();
  }
  public static void main(String args[]) {
    String str = "take u forward IS Awesome";
    int length = str.length();

    System.out.println("Resultant string: ");
    System.out.println(solve(str, length));
  }
}

Output:

Resultant string:
TAKE U FORWARD is aWESOME

Time Complexity: O(n)

Space Complexity: O(n), for StringBuffer

Solution 2: Using built-in functions

Approach:

Keep on iterating the given string:
If the corresponding character is uppercase then convert it to lowercase using built in functions described below
Else if the character is lowercase then convert it to uppercase using built in functions mentioned below.
If any whitespace then keep it as it is.
Return the final string

In C++,

towupper(): converts wide characters into uppercase

towlower(): converts wide characters into lowercase

In Java,

Character.toUpperCase(): converts the character argument to uppercase

Character.toLowerCase(): converts the character argument to lowercase

Code:

C++ Code

#include<bits/stdc++.h>

using namespace std;
void solve(string str, int n) {

  for (int i = 0; i < n; i++) {
    int ascii = (int) str[i];

    if (ascii >= 65 && ascii <= 90) // if uppercase
      str[i] = towlower(str[i]);

    else if (ascii >= 97 && ascii <= 122) // if lowercase
      str[i] = towupper(str[i]);

  }

  cout << "Resultant string: " << "\n";
  cout << str << "\n";
}
int main() {

  // Input string
  string str = "take u forward IS Awesome";
  int n = str.length();

  solve(str, n);
  return 0;
}

Output:

Resultant string:
TAKE U FORWARD is aWESOME

Time Complexity: O(n)

Space Complexity: O(1)

Java Code

public class tUf {
  public static String solve(String str, int n) {
    StringBuffer ans = new StringBuffer();
    for (int i = 0; i < n; i++) {
      int ascii = (int) str.charAt(i);

      if (ascii >= 65 && ascii <= 90) // if uppercase
        ans.append(Character.toLowerCase((char) ascii));

      else if (ascii >= 97 && ascii <= 122) // if lowercase
        ans.append(Character.toUpperCase((char) ascii));

      else if (str.charAt(i) == ' ') // if whitespace
        ans.append(' ');
    }

    return ans.toString();
  }
  public static void main(String args[]) {
    String str = "take u forward IS Awesome";
    int length = str.length();

    System.out.println("Resultant string: ");
    System.out.println(solve(str, length));
  }
}

Output:

Resultant string:
TAKE U FORWARD is aWESOME

Time Complexity: O(n)

Space Complexity: O(1)

Special thanks to Rishiraj Girmal for contributing to this article on takeUforward. If you also wish to share your knowledge with the takeUforward fam, please check out this article