[Seta00]

The format specifier for char is %c:

scanf("%c", &operator);

[Seta00]

I have no idea why, but it really didn't work on MinGW...
I suggest you to use the C++ libraries:

#include <iostream> // c++ input/output
using namespace std; // standard namespace

int main() {
    float num1, num2,output;
    char op;

    cout << "Enter a number: "; // equivalent to printf
    cin  >> num1;               // equivalent to scanf

    cout << "Enter another number: ";
    cin  >> num2;

    cout << "Press + to add, - to subtract, * to multiply, / to divide: ";
    cin  >> op;

    if(op == '+')
    {
        output =  num1 + num2;
    }
    else if(op == '-')
    {
        output =  num1 - num2;
    }
    else if(op == '*')
    {
        output  =  num1 * num2;
    }
    else if(op == '/')
    {
        output = num1 / num2;
    }

    cout << "Result = " << output;
    return 0;
}

[anonymouscodder]

Typical problem scanf + EOL.

Use this:

scanf(" %f", &num1); //Whitespace at the beginning of the string

Don't know if it's the right way to do it, but it should do the trick.

And the last one:

scanf("%f", &output);

Maybe you wanted to print the result right?

printf("%f", output);

[Seta00]

That's because you're printing output's address, not its value.

printf(" %f", &output);

should be

printf("%f", output);

[Seta00]

Then you're doing it very wrong.
Works perfectly for me, with only one modification: the removal of the & operator on the last printf call.

[anonymouscodder]

Instead of the whitespace trick you can use:

fflush(stdin);

But I'm pretty sure that way is a bad habit.

Anyway, I tried your code and worked fine here (mingw).

[Seta00]

c.user, on 22 September 2010 - 05:27 PM, said:

fflush() can be used only for output streams, stdin is an input stream

This is not true. The only thing about using it on input streams is the functionality isn't guaranteed on all platforms.
On all major implementations, it means clear the buffer.

[Oler1s]

Quote

This is not true. The only thing about using it on input streams is the functionality isn't guaranteed on all platforms.

To be correct, calling fflush with an input stream as an argument is an undefined operation. Which more or less means don't do it.

It's very few lines to portably and cleanly extract from the stream. Wrap that functionality into your own function and call that instead.

[anonymouscodder]

I did know that fflush(stdin) was a bad habit, didn't remember why.

Apparently, this EOL problem with scanf only appears when reading a char.

If the whitespace trick didn't work, you can try something like this:

char c;
scanf("%c%c", (char*)malloc(sizeof(char)), &c);

or

char c, aux; //Won't use aux value
scanf("%c%c", &aux, &c);

To use the malloc version remember to include stdlib.h or malloc.h.

This post has been edited by anonymouscodder: 22 September 2010 - 08:49 PM