C Program to Sort Array of Strings in Alphabetical Order

Problem: Write a program in C to sort an array of strings or names in alphabetical order.

Input:  {"Ball", "Apple", "Cat"}
Output: {"Apple", "Ball", "Cat"}

We can easily sort an array of strings in C using the bubble sort algorithm.

We compare the adjacent strings using the strcmp() method inside the nested ‘for’ loops and swap them if they are in the wrong order (i.e. if strcmp() returns a value greater than 0.).

strcmp(string1, string2) method compares the two strings lexicographically and returns the difference between them.

1. Returns 0 if strings are identical

2. Returns +ve difference if string1 > string2

3. Reruns -ve difference if string1 < string2

The algorithm to sort an array of strings in C is as follows:

1. Create an array of string and initialize it with the values.
2. For loop from i=0 to i<size_of_array:
   1. Nest another for loop from j=0 to j<size_of_array-i-1:
      1. Check if(strcmp(array[j], array[j+1]) > 0):
         1. If yes, then swap(array[j], array[j+1])
   2. End nested loop.
3. End outer loop.
4. Output the array.

Here is the implementation of the algorithm in C:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define size_of_array 3  //define size of the array
 
//function to display array
void display(char array[][30]){
  for(int i=0; i<size_of_array; i++){
    printf("%s ", array[i]);
  }
  printf("\n");
}
 
int main()
{
  //create an array of strings
  char array[size_of_array][30];

  //Inputting names
  printf("Enter %d Strings: \n", size_of_array);
  for(int i=0; i<size_of_array; i++){
    scanf("%s", array[i]);
  }

  //display the original array
  printf("Original array: ");
  display(array);

  char temp[30];

  //Sort array using the Buuble Sort algorithm
  for(int i=0; i<size_of_array; i++){
    for(int j=0; j<size_of_array-1-i; j++){
      if(strcmp(array[j], array[j+1]) > 0){
        //swap array[j] and array[j+1]
        strcpy(temp, array[j]);
        strcpy(array[j], array[j+1]);
        strcpy(array[j+1], temp);
      }
    }
  }

  //display the sorted array
  printf("Sorted Array: ");
  display(array);

  return 0;
}

Output:

Enter 3 Strings:
Ball Apple Cat
Original array: Ball Apple Cat
Sorted Array: Apple Ball Cat

In the above program, we have predefined the size of the array equal to 3 using the #define command.

We input values into the array and sort them in dictionary order following the Bubble Sort algorithm.

We have used strcpy() method to copy the string values from one array index to another in order to swap them.

In this tutorial, we learned to sort an array of strings in the C programming language.