Variable Multiplication in C?

Question

//Hydroelectric Dam Helper
#include <stdio.h>
#define GRAV 9.80
#define EFINC 0.9
#define EFINC2 90


int main()
{
  //Defines all the variables to be used
  double height, work, mass;
  printf("Height of dam (in meters):");
  scanf("%lf", &height);
  printf("Flow of water (in thousand cubic meters per second):");
  scanf("%lf", &mass);
  work = (mass * GRAV * height * EFINC); 
  printf("The dam would produce %f megawatts at %d%% efficency", &work, EFINC2);
  return 0; 
}

The values set correctly, I tested it by having it print height and mass but work never receives a value, and EFINC2 prints out a ridiculous number that I'm not really sure about

Answer 1

printf("The dam would produce %f megawatts at %d%% efficency", &work, EFINC2);

should read:

printf("The dam would produce %f megawatts at %d%% efficency", work, EFINC2);

&work is a pointer to work, i.e. a double* but for printf to print the value you need to pass a double and not a pointer. On your platform a double* is probably a different size to a double causing the subsequent printf formats to use the wrong data.

Answer 2

The problem is that you are having printf output a float with the %f specifier but passing in a double* via &work. Just remove the & and it should work fine.

printf("The dam would produce %f megawatts at %d%% efficency", work, EFINC2);

Answer 3

The reason why you are receiving a "ridiculous number" is that you are passing the address of work to printf(). Change &work to work and it should work properly.

Answer 4

Sure. The ampersand & in the printf-line means that the address of the variable work is read instead of the value

Answer 5

Try appending a d to the constants to force c to not cast to int might work. You could also try explicitly casting the values to either float or double.

Answer 6

you have given &work which is the address of work variable in memory, so it doesn't print any absurd value, it prints the memory location of work.

You should remove & from &work to receive value of work variable.

printf("The dam would produce %f megawatts at %d%% efficency", work, EFINC2);