如预期，IF声明

Question

if (Mileage > 0) do
    {
        calculateMileage();
        cout << "The cost of shipment over " << setprecision(2) << Mileage << " miles is \234" << variableShippingCost << ".";
        cout << "\n \n";
        system("pause"); //to hold the output screen
        return(0);
    }
    else
    {
        cout << "\n ERROR: The distance should be a positive value.";
        system("pause"); //to hold the output screen
        return(0);
    }

I have no clue why but Visual Studio 12 is bringing an error on the else saying that it expects a while. I've done many if else statements before and also in this program that work fine so could anyone help me to understand why in this case it is not happy?

Answer 1

The correct syntax is:

if (...) 
{...} else {...} 

when using if and

do {...}
while (...);

when using do...while .

There's no if() do statement in C/C++!

Answer 2

You have a do after the if , so the compiler expects a while after the do block.

if (Mileage > 0)
{
    do
    {
        calculateMileage();
        //etc...
    } while (something);
}
else
{
    //etc...
}

or

if (Mileage > 0) // no `do` here
{
    calculateMileage();
    //etc...
}
else
{
    //etc...
}

Answer 3

dont use do. that is for a while loop and the correct syntax for using that is

do{
...code here...
} while(some condition is true)

what you want is

if (Mileage > 0) //there is an implicit then here no need to do anything here
{
    calculateMileage();
    cout << "The cost of shipment over " << setprecision(2) << Mileage << " miles is \234" << variableShippingCost << ".";
    cout << "\n \n";
    system("pause"); //to hold the output screen
    return(0);
}   //<<<------if you really wanted to use the do (which you shouldnt) put a while here.
else
{
    cout << "\n ERROR: The distance should be a positive value.";
    system("pause"); //to hold the output screen
    return(0);
}

Answer 4

Because you are doing it wrong! C++ has if-else statements and do-while statements. do expects a while following itself, meanwhile while can be used independently. Similarly, if can be used independently, but else expects an if before itself.