Problem counting how many times a character repeats in a given string

Question

I have a problem solving an exercise to determine how many times a character repeats in a string:

In this challenge, you must implement the `vezesLetraAparece`function, which:

• Receives 2 parameters: frase, which must be a string and letra, another string;
• Return the number of times the letter appears in the sentence.

Complete the function vezesLetraAparece down below.

• The function is expected to return an integer number.
• The function accepts the following parameters:
  1. frase (string)
  2. letra (string)

The code I made is like this, but it’s not working.

function vezesLetraAparece(frase, letra) {
  var resultado = [ ];
  for (var letra = 0; letra < frase.length; letra++); {
    resultado.push (frase[letra])
  }
}

Why? How can I correct it?

Answer 1

The first problem is that you are not returning anything from the function vezesLetraAparece. Note that there is no statement return in the body of the function and, because of this, it at all times will return undefined.

Therefore by placing a return to return the value of resultado after the loop for finish, we’ll have something like this:

function vezesLetraAparece(frase, letra) {
  var resultado = [];

  for (var letra = 0; letra < frase.length; letra++) {
    resultado.push (frase[letra]);
  }
  
  return resultado;
}

console.log(vezesLetraAparece('abcaba', 'a'));

But by executing the code, we realize there’s another mistake. The code is not actually returning the number of times the letter passed in the 2nd argument occurs in the string. The for is simply splitting the string into an array, each element being a character.

Therefore, it is perceived that using an array as a result (or accumulator), in this case, does not make much sense. You also have to check if the letter corresponding to the current iteration matches (is equal) to the one that interests us. You’re not doing that check either.

Anyway, we need to use a number (which we will start as 0) as an accountant and a declaration if to count only the letters that are equal to the one we seek.

We will then:

function vezesLetraAparece(frase, letra) {
  var resultado = 0;

  for (var indiceLetra = 0; indiceLetra < frase.length; indiceLetra++) {
    if (frase[indiceLetra] === letra) {
      resultado++; // Somamos 1 ao contador.
    }
  }
  
  return resultado;
}

console.log(vezesLetraAparece('abcaba', 'a')); // 3

Also note that I had to rename the variable letra (in the for) for indiceLetra. If the name continued as letra, we would be over-writing the parameter letra, declared in function. This is called variable shadowing and in that case it is undesirable.

It also had an extra semicolon after for. Like him prevents the block of the for to be executed, we must remove it.

---

To simplify the for a little (and, breaking, deal with a possible problem linked to the "decomposition" of certain Unicode characters), you can use a loop for..of:

function vezesLetraAparece(frase, letra) {
  var resultado = 0;

  for (const letraAtual of frase) {
    if (letraAtual === letra) {
      resultado++;
    }
  }
  
  return resultado;
}

console.log(vezesLetraAparece('abcaba', 'a')); // 3

^{Obviously there are several other ways to solve this problem. These are just two of countless possibilities. As you learn more about Javascript, you’ll be able to think of other ways to solve it. Nevertheless, they are probably the simplest. :)}