When to use 'if' vs 'switch' statements?

Question

I am pretty new with coding and compiling small programs in C and I have looked at the multiple threads regarding this issue and yet still haven't found or understood the answer I am looking for. I guess could someone explain in terms a kindergartener would understand, Why an if statement would be better than a switch or vise versa?

The reason I'm asking is because I find it easier mentally, to accomplish the task in a switch vs an if.

Should I practice more if's?

Without getting me lost in complex issues, will there be scenarios where switch cases will not work later on in complex programming?

The example I have is I choose to make a Celsius to Fahrenheit conversion with a switch instead of an if. Was this a "poor choice"?

Any feed back would be greatly appreciated especially if I can grasp the answer given.

Here's my code

{
int cel, fah;
char answer = 0;

printf("What would you like to convert from? Type: 'C' Celsius / 'F' for Fahrenheit\t");
scanf(" %c", &answer);

switch(answer){

    case 'C':
    case 'c':
        printf("Enter Temperatur in Celsius:\t");        
        scanf("%d", &cel);

        fah = (cel * 1.8) + 32;

        printf("The Temperature in Fahrenheit is: %d\t\n", fah);
    break;

    case 'f':
    case 'F':
        printf("Enter Temperature in Fahrenheit:\t");
        scanf("%d", &fah);

        cel = (fah - 32) / 1.8;

        printf("The Temperature in Celsius is: %d\t\n", cel);
    break;

    default:
        printf("ERROR!!!\n");
}

return 0;

Answer 1

Without getting me lost in complex issues, will there be scenarios where switch cases will not work later on in complex programming?

In theory, you can frame any if-else block with either a single switch statement or nested switch statements.

In practice, a switch statement works well with a single integral value.

---

N.B. What follows is a matter of opinion.

If you have multiple conditional statements, such as:

if ( a > 10  )
{
   ...
}
else if ( b <= 25 )
{
   ...
}
else
{
   ...
}

use of switch statements is not the right approach.

If you are able to branch based on an integral value and there are more than 2 branches, it is better to use a switch statement.

Example 1

if ( a == 10 )
{
    doThis();
}
else
{
   doThat();
}

is better than

switch (a)
{
   case 10:
      doThis();
      break;

   default:
     doThat();
}

Example 2

switch (a)
{
   case 10:
      do10();
      break;

   case 20:
      do20();
      break;

   case 30:
      do30();
      break;

   default:
     doDefault();
}

is better than

if ( a == 10 )
{
    do10();
}
else if ( a == 20 )
{
    do20();
}
else if ( a == 30 )
{
    do30();
}
else
{
   doDefault();
}

Answer 2

if (either compare values are not integer types) Use_if();
else if (both compare values are variables or maybe in the future ) Use_if();
else if (code is easier to understand as if) Use_if();
else if (code is easier to understand as switch) Use_switch();
else if (code guidelines suggest prefer if) Use_if();
else if (code guidelines suggest prefer switch) Use_switch();
else if (many constants are used) Use_switch();
else Use_if();

Answer 3

To appreciate the difference between the two, consider the following two blocks of JS code that accomplish the same thing. One uses if statement and the other using switch statement. One can argue about the elegance and efficiency of one over the other.

Using if with else-if...

var name = "Wolverine";

if(name=="Spider-Man"){
    console.log("good guy!");
} 
else if(name=="Deadpool"){
    console.log("good guy!");
} 
else if(name=="Loki"){
    console.log("bad guy!");
}
else if(name=="Magneto"){
    console.log("bad guy!");
}
else if(name=="Wolverine"){
    console.log("good guy!");
}
else{
    console.log("hmm…");
}

Using switch...

var name = "Wolverine";
switch(name) {
    case "Spider-Man":
    case "Deadpool":
    case "Wolverine":
        console.log("good guy!");
        break;
    case "Loki":
    case "Magneto":
        console.log("good guy!");
        break;
    default:
        console.log("hmm…");
}

Answer 4

For your example, Celsius to Farenheit conversion, an 'if' is probably better to use than a switch, although there is nothing wrong with using a switch in terms of performance.

A switch basically just makes it easier to deal with situations in which you may have a wide variety of different choices to make based on the value of a given variable.

Let's say you have a variable which might have values A - Z, and for each possible value, you want to perform a different action. With if statements, you'll end up with a very long chain of conditionals:

if(value == 'A')
{ //do something
}
else if (value =='B'){
//do something else}
....
else{ //default}

A switch just makes this easier to deal with

switch(value){
case 'A':
  //do thing
  break;
case 'B':
  //do other thing
  break;
default:
  //default
  break;
}

For a variable with many possible values, the switch saves you time and effort, and is more readable.

For something with only two possible values though, like celsius and farenhiet, the switch isnt actually more readable or compact.

if(celsius)
{
//do thing
}else{
//do other thing
}

Is probably more readable than

switch(temperature){
case celsius:
 //do thing
 break;
case farenheit:
 //do thing
 break;
}

And faster/easier to code.

Logically, they are the same, but which one you use is really a matter of readability, effort, and time.