I'm getting a "conflicting types" error in C

I'm currently working on a program for a C course in开发者_如何转开发 which I have to output the area of a shape.

Here is a function for a rectangle's area that I have in my program:

double rectangle() // calculate area of rectangle
{
    double length, width;

    printf("\nEnter length and width of rectangle: ");
    scanf("%g %g\n", &length, &width);

    return (length*width);
}

here is where I call the function rectangle()

if(strncmp(shape, "rectangle", 15) == 0)
    area = rectangle();

I'm using Geany in Linux Mint with the GCC compiler.

The error I'm recieving is

"geometryv2.c:78: error: conflicting types for ‘rectangle’"

I don't see what's conflicting here. The function with return-type double is returning a double. Any help here would be greatly appreciated. I am still pretty new to C and this is actually my first C program.

Thanks!

Have you declared the function rectangle() before it is used? If not, it will be assumed to return an int.

You need a line like:

double rectangle(void);

somewhere before you call it, or to define the function in the same module from which it is called, before it is called.

What is data type of area variable ?

also fix scanf:

scanf("%lg %lg")