Expected Primary Expression Before Float

andrewb (5)
I am running into errors when I am compiling code in CodeBlocks, and I am not sure what I am doing wrong. I am creating this simple program for a class, but it is pulling up an error saying on line 27 (I have bolded it in the code): "error: expected primary-expression before 'float' for all 3 variables. Someone help me with this? I'm completely lost.


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#include <iostream>
#include <string>
#include <iomanip>
using namespace std;

float mileage(float startMiles, float endMiles, float gallonsUsed);

int main()
{
    float startMiles;
    float endMiles;
    float gallonsUsed;
    float mpg;

    // floating point output format
    cout << fixed << showpoint << setprecision(2);

    // collect data
    cout << "Enter starting mileage: " << endl;
    cin >> startMiles;
    cout << "Enter ending mileage: " << endl;
    cin >> endMiles;
    cout << "Enter number of gallons of gas used: " << endl;
    cin >> gallonsUsed;

    // calculate mileage
    mpg = mileage(float startMiles, float endMiles, float gallonsUsed);

    // output collected data
    cout << "for a trip with:" << endl;
    cout << "     " << gallonsUsed << "  gallons of gas used" << endl;
    cout << "    and a starting mileage of " << startMiles << endl;
    cout << "     and an ending mileage of " << endMiles << endl;
    cout << "     the mileage per gallon is " << mpg << endl;



    return 0;
}
MikeyBoy (5631)
That's not the correct syntax for calling a function. I strongly recommend you go back to your textbook and learn how to call a function properly, because it's absolutely fundamental to being able to program.
andrewb (5)
Well, are you supposed to call the function in int main()? or before it?
MikeyBoy (5631)
What do you mean, "before it"? You can't call anything before main - it's the entry point to your program!
andrewb (5)
I guess I'm very confused then because in my instructor's sample code, "float mileage" was called before main. I'm going to have to read this textbook again.
MikeyBoy (5631)
I suspect what you actually saw was a function declaration. That's not a call.

But yes, I'd strongly advise going back to your textbook to be absolutely clear in your mind what the difference between the two things is.
andrewb (5)
ok. thanks for the help
andrewb (5)
I just adjusted the code to how I am used to programming. Is this still sufficient? It runs and outputs the desired results.


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#include <iostream>
#include <string>
#include <iomanip>
using namespace std;

int main()
{
    float startMiles;
    float endMiles;
    float gallonsUsed;
    float mpg;

    // floating point output format
    cout << fixed << showpoint << setprecision(2);

    // collect data
    cout << "Enter starting mileage: " << endl;
    cin >> startMiles;
    cout << "Enter ending mileage: " << endl;
    cin >> endMiles;
    cout << "Enter number of gallons of gas used: " << endl;
    cin >> gallonsUsed;

    // calculate mileage
    mpg = (endMiles - startMiles)/gallonsUsed;

    // output collected data
    cout << "for a trip with:" << endl;
    cout << " " << gallonsUsed << " gallons of gas used" << endl;
    cout << "starting mileage of: " << startMiles << endl;
    cout << "ending mileage of: " << endMiles << endl;
    cout << "the mileage per gallon is: " << mpg << endl;



    return 0;
}


I just didn't understand what he was doing by declaring a variable like that up above main. I couldn't see what he wanted to do with it, so I just removed the mileage variable and set the mpg to what mileage would have been.
Last edited on
MikeyBoy (5631)
Well, it looks like it'll work fine, although it no longer calls a function to do the calculation. If the purpose of the exercise was to learn about functions, then it's probably not much use now ;)

I just didn't understand what he was doing by declaring a variable like that up above main. I couldn't see what he wanted to do with it, so I just removed the mileage variable and set the mpg to what mileage would have been.


mileage isn't a variable - it's a function. That bit above main is declaring a function called mileage, and declaring which arguments it takes and what it returns.
Last edited on
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