for (int letter = 0; letter < randomString.length(); letter++) {
 // your same code goes here
}

package test;
 
import java.util.Scanner;
 
class Project5B {
  public static void main(String[] args) {
    //1. Set up all variables(set some values of the variables)
    // These variables are moved inside do-while loop so that if
    // user wants to start over by typing 1 then all of these values
    // are reinitialized to zero
    int numOfA = 0; //a,A
    int numOfE = 0; //e,E
    int numOfI = 0; //i,I
    int numOfO = 0; //o,O
    int numOfU = 0; //u,U
    int numOfOther = 0; //other characters
 
    int control = 1; //control is the variable used with the while loop
    int i = 0; //i is the variable used to count in the char.At if statement
    String randomString = " "; //user input string
    char charLetter; //sets up the char for the for and nested ifs
 
    //2. Set up the loop for user end function
    do {
      numOfA = 0; //a,A
      numOfE = 0; //e,E
      numOfI = 0; //i,I
      numOfO = 0; //o,O
      numOfU = 0; //u,U
      numOfOther = 0; //other characters
 
      //3. Set up the scanner and scan the string from user
      Scanner scan = new Scanner(System.in);
      System.out.print("Enter a string: ");
      randomString = scan.next();
 
      //4. Determine the various information about the string
      for (int letter = 0; letter < randomString.length(); letter++) {
        charLetter = randomString.charAt(letter);
 
        if (charLetter == 'a' || charLetter == 'A') {
          numOfA++;
        }
        else if (charLetter == 'e' || charLetter == 'E') {
          numOfE++;
        }
        else if (charLetter == 'i' || charLetter == 'I') {
          numOfI++;
        }
        else if (charLetter == 'o' || charLetter == 'O') {
          numOfO++;
        }
        else if (charLetter == 'u' || charLetter == 'U') {
          numOfU++;
        }
        else {
          numOfOther++;
        }
      }
 
      //5. Print that which was determined
      System.out.println("\nNo. of 'A' / 'a' = " + numOfA);
      System.out.println("No. of 'E' / 'e' = " + numOfE);
      System.out.println("No. of 'I' / 'i' = " + numOfI);
      System.out.println("No. of 'O' / 'o' = " + numOfO);
      System.out.println("No. of 'U' / 'u' = " + numOfU);
      System.out.println("No. of non-vowels = " + numOfOther);
 
      //6. Scan for the user end function interger
      System.out.println(
          "If you would like to run the program for another string please enter 1.");
      control = scan.nextInt();
    }
    while (control == 1);
    // {
    //  ;
    //}
  }
}