Approach

Written by Simon Nguyen from CSESoc Education

The aim of the problem is to reverse a string. To reverse a string, there are 3 steps: Storing the string input into an array, creating a function to reverse the string, and printing the reversed string.

  1. Storing the string input in an array. See main(void).
    • To store a string in an array, create an array of type char that has the size of the maximum string length input.
    • Once you create your array, use fgets() to store the string input into the array.
char word[MAX_SIZE];
fgets(word, MAX_SIZE, stdin);
  1. Create a helper function to reverse the string. See reverse_function().
    • When we reverse a string, the first character becomes the last character, the second character becomes the second last character, and so on.
    • Hence, for a string of length N, we need to create a function that swaps the 1st and Nth character, the 2nd and (N-1)th character, until the (N/2)th swapped is reached.
      • For strings of even length, the (N/2)th swap will swap the 2 middle characters
      • For strings of odd length, the (N/2)th swap will swap the 2 adjacent characters to the middle character.
    • How do you find the length N of a string? Use strlen(array_name_of_string).
      • Note strlen() returns an int, where it will calculate length of string + new_line character from fgets().
      • For example, if the user inputs Hello and presses enter, strlen() will return 6 (5 for length of string + 1 for newline character).
    • Hence for an ith element in the string array, we want to swap it with the (N - 2 - i)th element in same array.
      • N - 2 - i = N - 1 - 1 - i
      • -1 so we dont consider the newline character
      • -1 to account for array indexing starting at 0.
    • Once we account for the condition above, we are simply swapping the ith character from the start and end of the string.
      • word[i] = word[L - i], where L = N - 2 (L is the last index of the string in array).
    • To swap numbers, we need to introduce a 3rd variable called a placeholder.
void reverse_function(char word[MAX_SIZE]) {
    int i = 0;
    int holder;
    while (i < strlen(word)/2) {
        holder = word[i];
        word[i] = word[strlen(word) - 2 - i];
        word[strlen(word) - 2 - i] = holder;
        i++;
        
    }
     
}
  1. Print the reversed string. See main(void).
    • To print a string, use printf(ā€œ%sā€, array_name_of_string), where %s is the format specifier for a string.