Switch statements range of numbers in c-CodePudding

I have an assignment from my instructour he asked me to use switch statements to determine the age of the person, but I cannot find the error here, I did the same as I learned.

    //check user age
// error begins here
    switch (age)
    {
        case 0 ... 10:
            puts("You are less than 10");
            break;
        case 10 ... 20:
            puts("You are in your tens");
            break;
        case 20 ... 30:
            puts("You are in twenties");
            break;
        case 30 ... 40:
            puts("Your are in thirties");
            break;
        case 40 ... 50:
            puts("Your are in fourties");
            break;
        case 50 ... 60:
            puts("Your are in fifties");
            break;
        case 60 ... 70:
            puts("Your are in sixties");
            break;
        case 70 ... 80:
            puts("Your are in seventies");
            break;
        case 80 ... 90:
            puts("Your are in eighties");
            break;
        case 90 ... 100:
            puts("Your are in nineties");
            break;
        case 100:
            puts("Your are a 100  !!");
            break;
    
    }

**Errors by the compiler are ** :

Lab2_3.c:48:9: error: this is the first entry overlapping that value
         case 80 ... 90:
         ^~~~

CodePudding user response：

You can't use the switch statement for arbitrary ranges.

But since you only need to test decades, you can divide the age by ten to compare them.

switch (age/10)
{
    case 0:
        puts("You are less than 10");
        break;
    case 1:
        puts("You are in your tens");
        break;
    case 2:
        puts("You are in twenties");
        break;
    case 3:
        puts("Your are in thirties");
        break;
    case 4:
        puts("Your are in fourties");
        break;
    case 5:
        puts("Your are in fifties");
        break;
    case 6:
        puts("Your are in sixties");
        break;
    case 7:
        puts("Your are in seventies");
        break;
    case 8:
        puts("Your are in eighties");
        break;
    case 9:
        puts("Your are in nineties");
        break;
    default:
        puts("Your are a 100  !!");
        break;

}

CodePudding user response：

case 0 ... 10: is not portable C. Perhaps some compilers may support it as an extension.

Makes sense not to overlap the range

    case 0 ... 9: // not 10
        puts("You are less than 10");
        break;
    case 10 ... 19: // not 20
        puts("You are in your tens");
        break;
  ...

Instead of using a non-standard switch, case, consider:

if (age < 0) {
  puts("You are less than 0");
} else if (age < 10) {
  puts("You are less than 10");
} else if (age < 20) {
  puts("You are in your tens");
...

If a switch is still required:

    case 0:
    case 1:
    case 2:
    case 3:
    case 4:
    case 5:
    case 6:
    case 7:
    case 8:
    case 9:
        puts("You are less than 10");
        break;
    case 11:
    case 12:
    ...

Or perhaps

if (age < 0) {
  puts("You are less than 0");
} else if (age < 100) {
  static const char *string_lookup_table[10] = {
    "less than 10", 
    "in your tens", 
    ...
  };
  int decade = age/10;
  printf("You are %s\n", string_lookup_table[decade]);
} else  {
  puts("You are a 100  !!");
}

Note: `"your" should be "you".

CodePudding user response：

First of all, please note that so-called "case ranges" is not valid standard C, but a non-standard gcc extension. As such, practicing to using them as a beginner is questionable at best. You will need to use the gcc compiler and use it in "lax" mode, without any -std=cxx or -pedantic flags. -std=gnu17 explicitly enables these kind of extensions.

As for the compiler errors, they are pretty self-explanatory. You have overlapping ranges, which isn't allowed by this extension. You need to do 0 ... 9 then 10 ... 19 and so on.

Algorithm-wise, ask yourself if a 10 year old is less than 10 years old. Is a 30 year old really in their twenties, and so on. That is not a programming problem.

Regarding your options to do this in valid standard C, see the answer by @chux.