Compute sum and subtraction in Javascript

Question

I’m a beginner in programming and I’m starting with Javascript and I need to solve the following question that is not presenting an adequate result when performing the subtraction: add the two numbers if you have the +, subtract if you have the - or return "none of the options" if the sign is neither of these two.

I wrote it this way:

var somaSubtracao;
function somaSubtracao(num1, num2) {
    if (somaSubtracao = "+") {
        return num1 + num2;
    } if (somaSubtracao === "-") {
        return num1 - num2;
    } else {
        return "nenhuma das opções";
    }
}
console.log(somaSubtracao);

Answer 1

Basically failed to pass in the function the type of operation and at the time of the method call pass what operation you want to do, example:

function somaSubtracao(num1, num2, operacao) {
    if (operacao === "+") return num1 + num2;
    if (operacao === "-") return num1 - num2;
    return "nenhuma das opções";    
}

console.log(somaSubtracao(10, 20, '+'));
console.log(somaSubtracao(40, 20, '-'));
console.log(somaSubtracao(10, 20, ''));

Answer 2

I believe that, unless typing error, your intention was to compare someone to a value but in fact you are assigning a value to someone if (somaSubtracao = "+")

Equal sign assigns and two equals sign compares there are still 3 signs of equal === which means strictly equal (checks content and type of variable).

When a function receives parameters, it assigns the values received to the variable names specified in the parentheses of the function definition. Consider the following script segment:

function somaSubtracao(num1) {
  console.log(num1);
}
somaSubtracao(3);

After the function is defined, the next statement calls that same function, passing the number 3. somaSubtracao(3); and the function will assign that value to the variable num1 and accomplish something with it.

In defining its function you should expect 3 parameters, that is, two numbers and a third one whose value will indicate what to do with the numbers passed, sum or subtraction.

function somaSubtracao(num1, num2, somaSubtracao) {

Thus the function lacked a third parameter that would be the operation between the other two parameters passed.

Done this call the function and pass the 3 parameters it expects, two numbers and a sign that represents sum or subtraction

  somaSubtracao(3, 6, '+');

The correct conditional structure is:

if (condição 1) {
   faça isso
} else if (condição 2) {
   faça isso
} else {
  faça isso
}

In your case it would be

function somaSubtracao(num1, num2, somaSubtracao) {
    if (somaSubtracao == "+") {
        return num1 + num2;
    } else if (somaSubtracao == "-") {
        return num1 - num2;
    } else {
        return "nenhuma das opções";
    }
}

console.log(somaSubtracao(3, 6, '+'));
console.log(somaSubtracao(3, 6, '-')); 
console.log(somaSubtracao(3, 6));

What? function name equal to variable name? This is the answer to another question :-)

Maybe you’d like to study a little more

function somaSubtracao(num1, num2) {
let Accum=0;
( !isNaN(num1) && !isNaN(num2) ) ? Accum=(num1+num2) : Accum=("nenhuma das opções");
return Accum;
}

 console.log(somaSubtracao(3, 6));
 console.log(somaSubtracao(3, -6)); 
 console.log(somaSubtracao(-3, -6));
 console.log(somaSubtracao(3));
 console.log(somaSubtracao('x', 3));

isNaN - used to check when it is not a number, so if you want to know if it is numeric you can use !isNaN. the symbol ! is negation, therefore the negation of não numérico is numérico

The expression ( !isNaN(num1) && !isNaN(num2) ) ? Accum=(num1+num2) : Accum=("nenhuma das opções"); is ternary conditional operator. It evaluates conditional expressions, in a manner similar to if, see this response from bfavaretto on ternary operator.

Answer 3

just complementing the above comment...

Note that you just declared the function, but have not yet used it.

function somaSubtracao(num1, num2, operacao) {
    if (operacao === "+") return num1 + num2;
    if (operacao === "-") return num1 - num2;
    return "nenhuma das opções";    
}

console.log(somaSubtracao(10, 20, '+'));
console.log(somaSubtracao(40, 20, '-'));
console.log(somaSubtracao(10, 20, ''));