What's wrong with this function? not assignable?

Question

float tempC(unsigned int adc_value) {
    multiplier = adc_value / 1023.0f;
    tempC = -40 * multiplier * 90;
    return tempC;
}

I am trying to use the ADC on a micro-controller to convert a potentiometer into temperature between -40 and 50 degrees C, the adc_value is the range given by the ADC however I get the error:

Main.c:110:11: error: non-object type 'float (unsigned int)' is not assignable

I can provide more code if needed but I don't know where I'm going wrong as I am quite new to C and programming.

Answer 1

tempC is not a variable but the function, so you cannot assign there.

You should declare another variable instead of that like this:

float tempC(unsigned int adc_value) {
    float tempC_ret;
    multiplier = adc_value / 1023.0f;
    tempC_ret = -40 * multiplier * 90;
    return tempC_ret;
}

Or you can return the calculated value directly like this:

float tempC(unsigned int adc_value) {
    multiplier = adc_value / 1023.0f;
    return -40 * multiplier * 90;
}