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From: Keith Thompson <Keith.S.Thompson+u@gmail.com>
Newsgroups: comp.lang.c
Subject: Re: max of 3
Date: Sat, 22 Aug 2020 16:41:57 -0700
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Keith Thompson <Keith.S.Thompson+u@gmail.com> writes:

> axel porin <porinaxel@gmail.com> writes:
>> Le samedi 22 août 2020 à 12:25:07 UTC+2, Bart a écrit :
>>> On 22/08/2020 10:54, Ben Bacarisse wrote:
>>> > axel porin <pori...@gmail.com> writes: 
>>> 
>>> >> int main(){ 
>>> >> int a=2,b=-4,c=6; 
>>> >> printf("%d ",max3(a,b,c)); 
>>> > 
>>> > I'm curious. Why not write 
>>> > 
>>> > printf("%d\n", max3(2, -4, 6)); 
>>> > 
>>> > ?
>>> I'm surprised at this advice. Presumably the intention is to eventually 
>>> have a, b and c populated by other means (eg. from the user), but values 
>>> are currently hardcoded. 
>>> 
>>> And maybe the values will be printed out first, or as part of the output: 
>>> 
>>> printf("Max3(%d, %d, %d) = %d\n", a,b,c, max3(a,b,c)); 
>>> 
>>> This all becomes harder with your suggestion.
>> what should i write to get the warnings
>
> It depends on what compiler and programming environment you're using,
> and you haven't told us that.
>
> Following this thread, you're still posting code that isn't
> indented properly.  If you're on a Unix/Linux-like system, read
> the documentation for the "indent" command; I suggest "indent -kr".
> Other systems are likely to have code formatters (perhaps even your
> text editor can do this).
>
> Here's your original program from the top of this thread:
>
> int max3(int a,int b,int c){
>     if(a<b)
>     if(b<c)
>     return c;
>     else
>     return b;
> }
>
> int main(){
>     int a=2,b=-4,c=6;
>    printf("%d ",max3(a,b,c));
> }
>
> Note that within the body of max3, every line is at the same indentation
> level, even though there are several logical levels.
>
> Here's my second draft of your program, with no semantic changes other
> than adding the required "#include <stdio.h>".  (If your actual program
> doesn't have that and you didn't get a warning for the call to printf,
> you also need to crank up the diagnostics on your compiler.  If you did
> have "#include <stdio.h>", please include it when you post.)
>
> #include <stdio.h>
>
> int max3(int a, int b, int c) {
>     if (a < b)
>         if (b < c)
>             return c;
>         else
>             return b;
> }
>
> int main(void) {
>     int a = 2, b = -4, c = 6;
>     printf("%d ", max3(a, b, c));
> }
>
> The indentation makes it much more obvious that you don't do anything if
> the first (a < b) condition is false.  And knowing that a < b doesn't
> tell you whether b or c is the maximum value.
>
> Some of the changes I've made are a matter of personal taste.  The
> language doesn't require white space in most contexts, but I like to add
> a certain amount to make the code clearer.  Others prefer or or less
> white space.  I like spaces around most operators ("a < b" rather than
> "a<b").  I also always put a space after each comma, and after "if"
> (primarily so that "if (condition)" doesn't look like a function call).
>
> "int main()" is better written as "int main(void)".  This is a minor
> point, and your compiler probably doesn't care.  (I could expound on
> this point at some length, but it's not relevant for now.)
>
> My personal preference is to (almost) *always* use curly braces for
> control statements (if, for, while, etc.).  It makes the code easier to
> read (at least for me), and can prevent errors when you later add more
> statements.  (It's a habit I picked up from Perl, which requires it.)
>
> Here's the program again with curly braces added:
>
> #include <stdio.h>
>
> int max3(int a, int b, int c) {
>     if (a < b) {
>         if (b < c) {
>             return c;
>         }
>         else {
>             return b;
>         }
>     }
> }
>
> int main(void) {
>     int a = 2, b = -4, c = 6;
>     printf("%d ", max3(a, b, c));
> }
>
> Using curly braces *and* correct indentation is a belt-and-suspenders
> approach.  It's not strictly necessary, but it means that an error in
> either the indentation or in the braces is likely to stand out.  It's
> for the benefit of the human reader, not for the compiler.  This version
> is still incorrect.
>
> Note that some programmers prefer to put the opening "{" on a line by
> itself, aligned with the closing "}".  Both styles are valid.
> Personally, I prefer putting the "{" on the end of the line.
>
> Now let's fix the code so it actually works.  I've taken the liberty of
> pretty much rewriting max3() from scratch.
>
> #include <stdio.h>
>
> int max3(int a, int b, int c) {
>     if (a >= b && a >= c) {
>         return a;
>     }
>     else if (b >= c) {
>         return b;
>     }
>     else {
>         return c;
>     }
> }
>
> int main(void) {
>     int a = 2, b = -4, c = 6;
>     printf("%d\n", max3(a, b, c));
> }
>
> Look at the way the logic flows.  Either a, b, or c has the maximum
> value (perhaps more than one of them if there are duplicates).
> We first check whether a has the maximum value.  If it doesn't,
> we check whether b has the maximum value.  If it doesn't, c does.
>
> Note that I've added a newline "\n" to the printf call.  Output should
> (almost) always end with a newline character.
>
> As others have pointed out, you can also build max3 on top of a simpler
> max2 function:
>
> #include <stdio.h>
>
> int max2(int a, int b) {
>     if (a >= b) {
>         return a;
>     }
>     else {
>         return b;
>     }
>     // could also be:
>     // return a >= b ? a : b;
> }
>
> int max3(int a, int b, int c) {
>     return max2(max2(a, b), c);
> }
>
> int main(void) {
>     int a = 2, b = -4, c = 6;
>     printf("%d\n", max3(a, b, c));
> }

Here's another approach:

#include <stdio.h>

int max3(int a, int b, int c) {
    int result = a;
    if (b > result) result = b;
    if (c > result) result = c;
    return result;
}

void try(int a, int b, int c) {
    // Assumes arguments are 1, 2, and 3 in any order
    int result = max3(a, b, c);
    printf("max3(%d, %d, %d) = %d ", a, b, c, result);
    if (result == 3) {
        printf("OK\n");
    }
    else {
        printf("FAIL\n");
    }
}

int main(void) {
    try(1, 2, 3);
    try(1, 3, 2);
    try(2, 1, 3);
    try(2, 3, 1);
    try(3, 1, 2);
    try(3, 2, 1);
}

You'll notice that I didn't use curly braces in the if statements,
something I said I always do.  I sometimes make an exception for
statements that fit cleanly on one line, especially if there are
several of them in a row and I can format them legibly.

-- 
Keith Thompson (The_Other_Keith) Keith.S.Thompson+u@gmail.com
Working, but not speaking, for Philips Healthcare
void Void(void) { Void(); } /* The recursive call of the void */