Remove Characters in String Except Alphabets

#include <stdio.h>
int main(){
   char line[150];
   
   printf("Enter a string: ");
   fgets(line, sizeof(line), stdin); // take input


   for (int i = 0, j; line[i] != ''; ++i) {

      // enter the loop if the character is not an alphabet
      // and not the null character
      while (!(line[i] >= 'a' && line[i] <= 'z') && !(line[i] >= 'A' && line[i] <= 'Z') && !(line[i] == '')) {
         for (j = i; line[j] != ''; ++j) {

            // if jth element of line is not an alphabet,
            // assign the value of (j+1)th element to the jth element
            line[j] = line[j + 1];
         }
         line[j] = '';
      }
   }
   printf("Output String: ");
   puts(line);
   return 0;
}

Output

Enter a string: p2'r-o@gram84iz./
Output String: programiz

This program takes a string input from the user and stores in the line variable. Then, a for loop is used to iterate over characters of the string.