Mine

#include <stdio.h>

double add(double,double );
double subtract(double,double );
double multiply(double,double );
double divide(double,double );

void main (void)
{
	int choice;
	double x, y;
	double returned_sum;
	double returned_difference;
	double returned_product;
	double returned_quotient;
	
	printf("What would you like to do?\nPlease choose a number:\n");
	printf("1.\tAdd\n2.\tSubtract\n3.\tMultiply\n4.\tDivide\n");
	scanf("%d", &choice);

	printf("Please enter two numbers of type double\t");
	scanf("%lf%lf",x,y);

	if (choice==1)
	{
		returned_sum=add(x,y);
		printf("The sum of your two numbers %lf and %lf is %lf",x,y,returned_sum);
	}
	else if (choice==2)
	{
		returned_difference=subtract(x,y);
	}
	else if (choice==3)
	{
		returned_product=multiply(x,y);
		multiply(x,y);
	}
	else if (choice==4)
	{
		if (y!=0)
		{
			returned_quotient=divide(x,y);
		}
		else
			printf("You cannot divide by 0!");
	}
	else
	{
		printf("This is an invalid entry please choose one of the above numbers");
	}

}
double add(double x,double y)
{
	double sum;
	sum=x+y;
	return sum;
}
double subtract(double x,double y)
{
	double difference;
	difference=x-y;
	return difference;
}
double multiply(double x,double y)
{
	double product;
	product=x*y;
	return product;
}
double divide(double x,double y)
{
	double quotient;
	quotient=x/y;
	return quotient;
}