[SOLVED] Switch statement difficulties

[ruben91]

i have done an if statement in my project, it worked fine but quite laggy as it takes time to read, so i planned to change it to switch case statement bt i seem to get error i compiling, pls help me to solve this
here is my code

if(distance>=0 && distance<=250)
{
PORTDbits.RD2=1;
}

if(distance>=251 && distance<=500)
{
PORTDbits.RD3=1;
}

if (distance>=501 && distance<=1000)
{
PORTDbits.RD0=1;
}

if(distance>=1001)
{
PORTDbits.RD1=1;
}

this is my coverted switch statement
bt i get error in compiling

switch(distance)
{
case distance>=0 && distance<=250:
PORTDbits.RD1=1;
break;
case distance>=251 && distance<=500:
PORTDbits.RD2=1;
break;
case distance>=501 && distance<=1000:
PORTDbits.RD3=1;
break;
case distance>=1001:
PORTDbits.RD4=1;
break;
}

 

[ud23]

if(distance>=0 && distance<=250)
{
PORTDbits.RD2=1;
}

else if(distance>=251 && distance<=500)
{
PORTDbits.RD3=1;
}

else if (distance>=501 && distance<=1000)
{
PORTDbits.RD0=1;
}

else if(distance>=1001)
{
PORTDbits.RD1=1;
} 
else
{


}

your if statement should be like that and your switch conversion is totally wrong.

 

[kam1787]

if (distance>=0 )
{ 
if (distance<=250)
{
PORTDbits.RD2=1;
}

else if(distance<=500)
{
PORTDbits.RD3=1;
}

else if (distance<=1000)
{
PORTDbits.RD0=1;
}
else 
{
PORTDbits.RD1=1;
}
}

indentation is lousy but you get the idea

 

[betwixt]

In a switch/case statement the 'case' must equate to a constant, you can't use variables I'm afraid.
You might also need to consider what happens to the other outputs when the distance is not between the limits.

Brian.

 

[d3javu]

Switch case requires constant value, if you have predefined value, then can do like below(just an example), otherwise if else is the best i believe or do it in assembly to optimize the code.

switch(input){

    case 0:
    case 150:
    case 250:
                PORTDbits.RD2=1;
        break;

    case 400:
    case 500:
                PORTDbits.RD3=1;
        break;

      default:
                PORTDbits.RD1=1;   
}

 

[betwixt]

The other way you can optimize the code is to work from the highest value down using 'if' statements and put it in a function. It reduces the number of calculations needed to check the value.

For example:

void MyFunction()
{
 if(distance > 1000) {PORTDbits.RD4 = 1; return;}
 if(distance > 500) {PORTDbits.RD3 = 1; return;}
 if(distance > 250) {PORTDbits.RD2 = 1; return;}
 PORTDbits.RD1 =1;
}

which should do the same thing.

Brian.