How to reprompt after user inputs wrong number?

Would I have to do a loop of some sort?

I want my code to do this:

Enter a Compass Heading: 500.7
Please Input a Compass Heading between 0 and 360 Degrees.
Enter a Compass Heading: 360.0

If the user puts a number not in 0 - 360, I want the program to reprompt or start over again. How would I do that?

Yes, you need a loop.

Code:

---

int input_valid = 0;
while(!input_valid)
{
    input = get_input();
    input_valid = input >= 0 && input <= 360;
}

---

or...

Code:

---

while(!(input >= 0 && input <= 360;))
{
    input = get_input();
}

---

You could also interpret anything above 360 as 360, and anything below 0 as 0. Alternatively, interpret for example 500.7 as 140.7 degrees.

Alright, so I tried putting the above codes in and I keep getting errors. Where would I insert the while loop in my code?

Code:

---

/* Directives */

#include <stdio.h>

int main(void)
{

double heading; /*compass heading in degrees*/

/* Get compass heading */
printf("Enter a Compass Heading: ");
scanf("%lf", &heading);

/* Display equivalent compass bearing */
if (heading < 0.0)
printf("Please Input a Compass Heading between 0 and 360 Degrees.\n", heading);

else if(heading < 90.0)
        printf("Compass Bearing: North  %.1f Deg East\n", heading);

else if(heading <= 180.0)
        printf("Compass Bearing: South %.1f Deg East\n", 180 - heading);

else if(heading <= 270.0)
        printf("Compass Bearing: South %.1f Deg West\n", heading - 180.0);

else if(heading <360.0)
        printf("Compass Bearing: North %.1f Deg West\n", 360.0 - heading);

else
        printf("Please Input a Compass Heading between 0 and 360 Degrees.\n", heading);

/* End Program */
return(0);
}

---

Code:

---

do
    angle = get_angle();
while( angle < 0 || angle >= 360 );

---

But I agree with other posters that there is nothing inherently bad about a heading of 500.7. It's the same as a heading of 140.7.

(Note that heading isn't the same as rotation. A rotation of 500.7 degrees is not the same as a rotation of 140.7 degrees. In the first case the object makes an extra revolution.)

Quote:

---

Originally Posted by brewbuck

Code:

---

do
    angle = get_angle();
while( angle < 0 || angle >= 360 );

---

But I agree with other posters that there is nothing inherently bad about a heading of 500.7. It's the same as a heading of 140.7.

(Note that heading isn't the same as rotation. A rotation of 500.7 degrees is not the same as a rotation of 140.7 degrees. In the first case the object makes an extra revolution.)

---

Ok, so where would I put that code? And would I need to declare anything for the code?

I want the program to only take in 0-360 that's why I am asking for help to reprompt the user for 0-360.

Code:

---

printf("Enter a Compass Heading: ");
scanf("%lf", &heading);

---

Looks to me like that's the code that needs to be in a loop.

What we're saying is to out this whole thing inside a loop. Perhaps you could have a function which validates the current inputed value which returns a bool and use the return value to decide whether to prompt for the values again. Like

Code:

---

printf(" Prompt for a value ");
scanf( num )

while( inputvalidate( num ) )
{
      printf( "Prompt again!" );
      scanf( num );
}

or use do while

---

You could also camp the value to min and max if it goes beyond or bellow as its been suggested.

~ssharish

Thanks to everyone that helped me. I finally got it all working. I couldn't have done it without you guys.

Could you post the whole code, if you want?

Quote:

---

Originally Posted by yann

Could you post the whole code, if you want?

---

No problem.

Code:

---


/* Directives */

#include <stdio.h>

int main(void)
{

double heading; /*compass heading in degrees*/

/* Get compass heading */

do
{
printf("Enter a Compass Heading: ");
scanf("%lf", &heading);

/* Display equivalent compass bearing */

if (heading < 0.0 || heading > 360.0)
printf("Please Input a Compass Heading between 0 and 360 Degrees.\n", heading);
} while (heading < 0.0 || heading > 360.0);

if(heading <= 90.0)
        printf("Compass Bearing: North %.1f Deg East\n", heading);

else if(heading < 180.0)
        printf("Compass Bearing: South %.1f Deg East\n", 180 - heading);

else if(heading <= 270.0)
        printf("Compass Bearing: South %.1f Deg West\n", heading - 180.0);

else if(heading <360.0)
        printf("Compass Bearing: North %.1f Deg West\n", 360.0 - heading);

else if(heading == 360.0)
        printf("Compass Bearing: North %.1f Deg East\n", 360.0 - heading);
else
        printf("Please Input a Compass Heading between 0 and 360 Degrees.\n", heading);



/* End Program */
return(0);
}

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