How to set a pointer as the default parameter in C++?

Question

I am "programming in C", but compiling using the extension .cpp and the g++ to have some facilities. My goal is to make a program that receives a starting salary and calculates the final salary according to certain bonus. The bonus is given in percentage over the initial salary, and if the function is called without being passed a value for the bonus, it must assume the value of 15%.

What I did:

#include <cstdio>

float calculaSalario(float* salario, float* bonificacao = 15.0f);

int main (void)
{
    float salario = 0;
    float bonificacao = 0;

    scanf("%f", &salario);
    scanf("%f", &bonificacao);

    calculaSalario(&salario, &bonificacao);

    printf("%f\n", salario);

    return 0;
}

float calculaSalario(float* salario, float* bonificacao = 15.0f)
{
    *salario = *salario + *salario * (*bonificacao/100);
}

However, I am getting the following errors:

• error: could not float calculaSalario(float* salario, float* bonus = 15.0f);

• In function ‘float calculaSalario(float*, float*)’: error: default argument given for parameter 2 of ‘float calculaSalario(float*, float*)’ [-fpermissive] note: previous specification in ‘float calculaSalario(float*, float*)’ here float calculaSalario(float* salario, float* bonus = 15.0f);

Answer 1

The first obvious problem is use float for monetary value, may not. But by a tremendous misfortune does not generate error, only causes problems sometimes, and the programmer thinks it is right.

Another error is using pointer in this function, it makes no sense, mainly because it already predicts returning something. In fact what the function returns is not the salary, so the correct is not to keep in the same variable, works and is right, but it is more readable and organized to keep in a variable that is the salary bonus. It’s not cool to repurpose variable to something else.

#include <cstdio>

float calculaSalario(float salario, float bonificacao = 15.0) { return salario + salario * (bonificacao / 100); }

int main() {
    float salario = 0;
    float bonificacao = 0;
    scanf("%f", &salario);
    scanf("%f", &bonificacao);
    salario = calculaSalario(salario, bonificacao);
    printf("%f\n", salario);
}

Behold working in the ideone. And in the repl it.. Also put on the Github for future reference.