Reversing a string means changing its order so that the last character becomes the first, the second last character becomes the second, and so on. A while loop is a control flow statement used in R programming to execute a block of code repeatedly as long as a specified condition is true. By using a while loop, we can easily reverse a given string in various programming languages.
Example:
input string : geeks
reversed string : skeeg
Concepts related to the topic:
- Strings: A sequence of characters in programming, which can be manipulated and processed.
- While Loop: A control structure that repeatedly executes a block of code as long as a given condition is true.
- Indexing: The ability to access individual characters in a string using their position or index.
Steps needed:
- Initialize two variables, one for the original string and one for the reversed string.
- Start a while loop with the condition that the length of the original string is greater than 0.
- Inside the loop, extract the last character of the original string and append it to the reversed string.
- Remove the last character from the original string.
- Repeat steps 3 and 4 until all characters are processed.
- Print or return the reversed string.
Example 1 : Reverse a string using a while loop
R
reverseStr <- function (str) {
reversedStr <- ""
while ( nchar (str) > 0) {
reversedStr <- paste0 (reversedStr, substr (str, nchar (str), nchar (str)))
str <- substr (str, 1, nchar (str) - 1)
}
return (reversedStr)
} # Example usage str <- "Hello, R!"
reversedStr <- reverseStr (str)
print (reversedStr)
|
Output:
[1] "!R ,olleH"
-
Input: The function
reverseStr
takes a single argumentstr
, which represents the input string that you want to reverse. -
Variable Initialization: Inside the function, you initialize an empty string
reversedStr
to store the reversed version of the input string. -
While Loop: The
while
loop runs as long as the length of the input string (str
) is greater than 0. - Reversing the String: Inside the loop:
-
substr(str, nchar(str), nchar(str))
: Extracts the last character of the currentstr
. -
paste0(reversedStr, ...)
: Concatenates the last character to thereversedStr
, effectively reversing the string. -
str <- substr(str, 1, nchar(str) - 1)
: Removes the last character from thestr
. - Loop Continuation: The loop continues to extract characters from the end of the input string and build the reversed string until the input string becomes empty.
-
Return: After the loop completes, the function returns the
reversedStr
.
Example 2: Reverse a string using a repeat loop
R
reverseStr <- function (str) {
reversedStr <- ""
repeat {
if ( nchar (str) == 0) break
reversedStr <- paste0 (reversedStr, substr (str, nchar (str), nchar (str)))
str <- substr (str, 1, nchar (str) - 1)
}
return (reversedStr)
} # Example usage str <- "R is awesome!"
reversedStr <- reverseStr (str)
print (reversedStr)
|
Output:
[1] "!emosewa si R"
reverseStr <- function(str).
-
This line defines the function named
reverseStr
that takes one parameter,str
, which represents the input string. -
reversedStr <- ""
: -
Initializes an empty string named
reversedStr
. This variable will be used to store the reversed string. -
repeat { ... }
: -
This initiates a
repeat
loop, which is a type of loop that continues executing until thebreak
statement is encountered. -
if (nchar(str) == 0) break
: -
This checks whether the length of the string
str
is zero. If it is, the loop breaks because there’s nothing left to reverse. -
reversedStr <- paste0(reversedStr, substr(str, nchar(str), nchar(str)))
: -
This line takes the last character of the original
str
and appends it to thereversedStr
. -
The
paste0()
function is used to concatenate strings without adding any space or separator between them. -
substr(str, nchar(str), nchar(str))
retrieves the last character of the string. -
str <- substr(str, 1, nchar(str) - 1)
: -
This line modifies the original
str
by removing its last character. -
It uses the
substr()
function to extract characters from position 1 tonchar(str) - 1
.
Example 3: Reverse a string using a while loop with pointers
R
reverseStr <- function (str) {
reversedStr <- ""
ptr <- nchar (str)
while (ptr > 0) {
reversedStr <- paste0 (reversedStr, substr (str, ptr, ptr))
ptr <- ptr - 1
}
return (reversedStr)
} # Example usage str <- "Loop in R!"
reversedStr <- reverseStr (str)
print (reversedStr)
|
Output:
[1] "!R ni pooL"
reverseStr <- function(str).
-
This line defines the function named
reverseStr
that takes one parameter,str
, which represents the input string. -
reversedStr <- ""
: -
Initializes an empty string named
reversedStr
. This variable will be used to store the reversed string. -
repeat { ... }
: -
This initiates a
repeat
loop, which is a type of loop that continues executing until thebreak
statement is encountered. -
if (nchar(str) == 0) break
: -
This checks whether the length of the string
str
is zero. If it is, the loop breaks because there’s nothing left to reverse.
Article Tags :
Recommended Articles