Error: I value required as left operand of assignment

This is a discussion on Error: I value required as left operand of assignment within the C Programming forums, part of the General Programming Boards category; I am getting this error when compiling my program with quincy: Error: I value required as left operand of assignment ...

  1. #1
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    Error: I value required as left operand of assignment

    I am getting this error when compiling my program with quincy:
    Error: I value required as left operand of assignment
    Tthe program is meant to calculate how much parking costs based on the amount of hours in a park and what type of vehicle it is. the error is coming from my function definitions which i have just started to add in.
    Code:
    float calcCarCost (char vehicletype, int time, float car)
    {
    
     if ((time > MINTIME) && (time <= 3)) 
     calcCarCost =( CAR * time );
     
         
    }
    the error is on line 72 which is:
    calcCarCost =( Car * time);

    i should probably point out CAR is already defined as a constant with a numerical value given and time is previously asked to be input in when the program runs.

    i am pretty new to programming in general which is probably pretty obvious by now and im just wondering what is causing the problem. If any more information is needed just ask. Thanks in advance

  2. #2
    and the hat of wrongness Salem's Avatar
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    Code:
    float calcCarCost (char vehicletype, int time, float car)
    {
    
     if ((time > MINTIME) && (time <= 3)) 
     calcCarCost =( CAR * time );
     
         
    }
    You're trying to assign to your function name.

    ( CAR * time ) isn't valid syntax either.
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    Look up the keyword return; it is used to return a value from a function in C and C++.

    Edit: "I value" was likely "lvalue" with the first letter an L standing for "left value".

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    Registered User hk_mp5kpdw's Avatar
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    First, variables are typically passed into a function for a reason... such as they are going to be used in some way by said function. You have several arguments being passed into the function and only one of them (time) seems to be used. What is the point of the other variables? Do they really need to be passed into the function if they aren't going to be used? Or, is the function incomplete?

    Second, be aware that the language is case-sensitive. In your post you have a function argument car (all lower case), you have a variable CAR in the function body, and you have Car that is mentioned in your post. Which one is which? Is there a typo somewhere? The language rules would treat each of these as separate variables so you need to make sure you know what you're talking about.

    Thirdly, your function as written will only return a value when the condition (time > MINTIME) && (time <= 3) is met. This means that the compiler should complain with a message along the lines of "not all control paths return a value" since nothing will be returned from the function if your time argument is outside the range of (MINTIME,3].
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    Algorithm Dissector iMalc's Avatar
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    Quote Originally Posted by Salem View Post
    ( CAR * time ) isn't valid syntax either.
    Well lexically that's just the syntax for multiplication, and it's the lack of being able to successfully look up the symbol for CAR that is the semantic problem.

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    Master Apprentice phantomotap's Avatar
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    Well lexically that's just the syntax for multiplication, and it's the lack of being able to successfully look up the symbol for CAR that is the semantic problem.
    O_o

    This is C++; the statement in isolation can be almost anything and imply anything at all. Here, if you missed the note that `CAR' is a constant numeric value, the syntax is almost certainly invalid. (You also apparently missed the note because `CAR' and `car' are said to be intentionally two different things.) It can easily be assumed that `CAR' is a type also implying problems with case consistency or misunderstanding how to return an instance of a `CAR' object.

    [Edit]
    I'll explain for those who don't appreciate the problems of this form of mixed declarations and expressions.

    That is the syntax for a few different things. (Most obviously, pointer declaration syntax and the multiplication operator.)

    What it is semantically depends on "LHS" and "RHS".

    If `CAR' is a type, the syntax is a declaration and semantically you've declared a pointer to a `CAR' type. (With C++, it doesn't matter what `time' is in this case because the compiler will try to treat it as a declaration.)

    If `CAR' is a variable and `time' is a variable or literal alias, the syntax is the multiplication operator and semantically you've done whatever is appropriate to the types involved. (So, preferably, some form of multiplication is involved.)

    If `CAR' is a variable and `time' is not a variable or literal alias, the syntax is meaningless and the result semantically meaningless.

    This all before templates and the C inherited preprocessed are involved, but at that point you have to expand everything so isn't interesting to this case. To be clear, what the expression may actually be can depend on how the template was instantiated or what problems may be related to macro.
    [/Edit]

    Soma

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    Algorithm Dissector iMalc's Avatar
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    Ugh, my head is pounding. Should be very careful what I post when I'm sick.
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    Quote Originally Posted by phantomotap
    This is C++
    Actually, this is C. Yeah, I know, easy to forget which forum you're in around here. Maybe we need a different colour scheme or something.
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    Master Apprentice phantomotap's Avatar
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    Yeah, I know, easy to forget which forum you're in around here. Maybe we need a different colour scheme or something.
    O_o

    I guess I need to confess that I tripped over myself.

    I get tired of writing out the relevant C family so just listed C++.

    When I came back to explain I thought it was the C++ board because of my own post. ;_;

    Soma

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    yeah thanks i fixed all the problems and it works fine now. Thanks to everyone who gave some input

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