Can't seem to pass information between function and main - c

Question

I can't get my code to run properly. Here it is:
#include <stdio.h>
void intro_msg( );
float compass_value( );
float direction( );
int main ( void )
{
float compass;
intro_msg( ) ;
compass_value(compass );
direction(compass );
return ( 0 ) ;
}
void intro_msg(void)
{
printf("Welcome to the Compass Program \n \n");
}
float compass_value(compass )
{
printf("Please enter a value for the compass direction. (0 - 360 degress ) : ");
scanf("%f", &compass);
printf("You entered %f degrees \n" , compass);
return(compass);
}
float direction(compass)
{
if (compass >= 354.38 && compass <= 360.00){
printf("You are heading North \n");
}
else if (compass >= 0.0 && compass <= 39.37){
printf("You are heading North \n");
}
else if (compass >= 39.38 && compass <= 84.37){
printf("You are heading Northeast \n");
}
else if (compass >= 84.38 && compass <= 129.37){
printf("You are heading East \n");
}
else if (compass >= 129.38 && compass <= 174.37){
printf("You are heading Southeast \n");
}
else if (compass >= 174.38 && compass <= 219.37){
printf("You are heading South \n");
}
else if (compass >= 219.38 && compass <= 264.37){
printf("You are heading Southwest \n");
}
else if (compass >= 264.38 && compass <= 309.37){
printf("You are heading West \n");
}
else if (compass >= 309.38 && compass <= 354.37){
printf("You are heading Northwest \n");
}
else
{
printf("You did not enter a value between 0 - 360 degrees");
}
}
I'm trying to obtain a degree between 0 - 360 from the user, record it and then determine the direction they are facing (North, South, Northeast, etc.) but my value for compass is never being recording.
Immediately after asking the user for the value, I go to print the value and I get 0.0, not what the user entered. What am I doing wrong here?

Answer 1

I think you know that you are actually passing compass variable into compass_value() by value. Means that the change wont be reflected into the compass variable of the main function.
I see that you are returning the read value, but you dont recieve it into anything at the call to compass_value() in your main function. Try recieving it :
compass = compass_value(compass);

Answer 2

This should fix your problems
#include <stdio.h>
void intro_msg( );
float compass_value(float); // You had not specified Argument type
float direction(float); // You had not specified Argument type
int main ( void )
{
float compass;
intro_msg( ) ;
compass_value(compass);
direction(compass);
return ( 0 ) ;
}
void intro_msg(void)
{
printf("Welcome to the Compass Program \n \n");
}
float compass_value(float compass) // You did not specify type
{
printf("Please enter a value for the compass direction. (0 - 360 degress ) : ");
scanf("%f", &compass);
printf("You entered %f degrees \n" , compass);
return(compass);
}
float direction(float &compass) // You did not specify type, also made it a reference
{
if (compass >= 354.38 && compass <= 360.00){
printf("You are heading North \n");
}
else if (compass >= 0.0 && compass <= 39.37){
printf("You are heading North \n");
}
else if (compass >= 39.38 && compass <= 84.37){
printf("You are heading Northeast \n");
}
else if (compass >= 84.38 && compass <= 129.37){
printf("You are heading East \n");
}
else if (compass >= 129.38 && compass <= 174.37){
printf("You are heading Southeast \n");
}
else if (compass >= 174.38 && compass <= 219.37){
printf("You are heading South \n");
}
else if (compass >= 219.38 && compass <= 264.37){
printf("You are heading Southwest \n");
}
else if (compass >= 264.38 && compass <= 309.37){
printf("You are heading West \n");
}
else if (compass >= 309.38 && compass <= 354.37){
printf("You are heading Northwest \n");
}
else
{
printf("You did not enter a value between 0 - 360 degrees");
}
}
Now, the problems with your code were that you did not specify the argument type in the function declaration and definitions. You were also passing compass by value, due to which the value you were accepting from the user in compass_value was not being put into your compass in the main. So, It always showed north. To fix this, pass compass by reference as indicated.
If you don't want to pass by reference, this code will help you
#include <stdio.h>
void intro_msg( );
float compass_value(float ); // You had not specified Argument type
float direction(float ); // You had not specified Argument type
int main ( void )
{
float compass;
intro_msg( ) ;
compass=compass_value(compass ); // Since the function was returning a compass, assign that value to the compass in main()
direction(compass );
return ( 0 ) ;
}
void intro_msg(void)
{
printf("Welcome to the Compass Program \n \n");
}
float compass_value(float compass ) // You did not specify type
{
printf("Please enter a value for the compass direction. (0 - 360 degress ) : ");
scanf("%f", &compass);
printf("You entered %f degrees \n" , compass);
return(compass);
}
float direction(float compass) // You did not specify type
{
if (compass >= 354.38 && compass <= 360.00){
printf("You are heading North \n");
}
else if (compass >= 0.0 && compass <= 39.37){
printf("You are heading North \n");
}
else if (compass >= 39.38 && compass <= 84.37){
printf("You are heading Northeast \n");
}
else if (compass >= 84.38 && compass <= 129.37){
printf("You are heading East \n");
}
else if (compass >= 129.38 && compass <= 174.37){
printf("You are heading Southeast \n");
}
else if (compass >= 174.38 && compass <= 219.37){
printf("You are heading South \n");
}
else if (compass >= 219.38 && compass <= 264.37){
printf("You are heading Southwest \n");
}
else if (compass >= 264.38 && compass <= 309.37){
printf("You are heading West \n");
}
else if (compass >= 309.38 && compass <= 354.37){
printf("You are heading Northwest \n");
}
else
{
printf("You did not enter a value between 0 - 360 degrees");
}
}

Answer 3

In the declaration
float direction(compass)
what type do you think compass is? (Hint: it is not a float or double.)
Here is how I would write this program (tested):
#include <stdio.h>
#define ARRAY_SIZE(A) (sizeof A / sizeof A[0])
void intro_msg (void)
{
printf ("Welcome to the Compass Program\n\n");
}
float compass_value (void)
{
double direction;
int bad = 1;
do {
printf ("Please enter a value for the compass direction (0 to 360 degrees): ");
fflush (stdout);
if (1 == scanf ("%lf", &direction))
bad = 0;
} while (bad);
printf ("You entered %f degrees\n", direction);
return direction;
}
static const struct {
float lo, hi;
const char *name;
} dirs [] = {
{354.38, 360.0, "North"},
{ 0.0, 39.37, "North"},
{ 39.37, 84.37, "Northeast"},
{ 84.37, 129.37, "East"},
{129.37, 174.37, "Southeast"},
{174.37, 219.37, "South"},
{219.37, 264.37, "Southwest"},
{264.37, 309.37, "West"},
{309.37, 354.37, "Northwest"},
};
void direction (double compass)
{
int j;
for (j = 0; j < ARRAY_SIZE (dirs); ++j)
if (compass >= dirs [j] .lo && compass <= dirs [j] .hi)
{
printf ("Direction is %s\n", dirs [j] .name);
return;
}
printf ("Direction is not between 0 and 360 degrees.\n");
}
int main (void)
{
double compass;
intro_msg ();
compass = compass_value ();
direction (compass);
return 0;
}