Today's C/C++ Programming Tip :-)

Paramesh · #1 15-Dec-2005, 11:55

Friends,
Hope this thread will be very useful for all of us!

Here is a start:

Language: C
For people using the GNU Compiler:
Linux: GNU gcc compiler
Windows: Dev C++, Code::Blocks, MingW compiler

Ever think this is a C program?
buggy.c

CPP / C++ / C Code:

#include<stdio.h>
int main() {
    int x=10;
    printf("x = %d\n", x);
    int y=20;
    printf("y = %d\n", y);
    int z = x + y;
    int array[z];
    // What the heck??
    printf("z = %d\n", z);
    return 0;
}

If you compile this without any flags in linux, such as gcc buggy.c, dont expect any errors or warnings.
The compiler is so happy about it!
In Windows too, the program compiles fine, and the user thinks that the program is correct!

But Alas! The program is not a valid ANSI C program.
C is a procedure oriented language, and one has to declare the variables at the start. You cannot declare them in the middle.
Comment style: There are NO // comment in ANSI C standard.
And you cant use variable types for array initialization!.

So, we have to configure the compiler to identify and correct the errors in the program.
For that, there are three compiler flags:
-ansi This flag tells the compiler to enforce ANSI C standards
-pedantic More pedantic ansi, warnings for stuff you probably didn't mean.
-Wall Show all reasonable warnings (there are more).

So, you should make sure that it is running as a standard C compiler and not a GNU C compiler.
* gcc -ansi -pedantic makes it run as a standard C compiler
* gcc -ansi -pedantic -Wall makes it run as a standard C compiler and check for several types of errors

If you use an IDE such as Dev C++, then you can go to
Tools->Compiler Options and add the commands when calling the compiler. (See the attachment.)

Now, the following warnings and error messages appear:

Quote:

buggy.c: In function `main':
buggy.c:5: warning: ISO C90 forbids mixed declarations and code
buggy.c:7: warning: ISO C90 forbids mixed declarations and code
buggy.c:8: warning: ISO C90 forbids variable-size array `array'
buggy.c:9: error: parse error before '/' token
buggy.c:8: warning: unused variable `array'

Now, correct the errors and make the ANSI compiler happy.

Cheers,

Paramesh.

alcoholic · #2 16-Dec-2005, 19:49

Quote:

Originally Posted by paramesh

But Alas! The program is not a valid ANSI C program.
C is a procedure oriented language, and one has to declare the variables at the start. You cannot declare them in the middle.
Comment style: There are NO // comment in ANSI C standard.
And you cant use variable types for array initialization!.

All of them are allowed in new ISO stnadard for C(C9X)

I guess ur using an old compiler urself

Paramesh · #3 16-Dec-2005, 20:19

Language: C/C++
Level: Beginner

Dont use 0 before numbers.
Instead of using 010, use 10.

For example consider this example:

CPP / C++ / C Code:

 #include<stdio.h>
 int main() {
     int a[8] = { 000, 001, 010, 011, 100, 101, 110, 111 };
     int i;
     for(i = 0; i < 8; i++ ) {
         printf("%d\n", a[i]);
     }
     return 0;
 }

Expected output:

Code:

Actual Output:

Code:

Because Numbers that start with 0 are taken as Octal, so 010 is taken as 10-octal or 8-decimal.

So, we should be careful in using numbers.

Another example:

CPP / C++ / C Code:

 #include<stdio.h>
 int main() {
     int a[8] = { 0000, 0001, 0010, 0011, 0100, 0101, 0110, 0111 };
     int i;
     for(i = 0; i < 8; i++ ) {
         printf("%d\n", a[i]);
     }
     return 0;
 }

As expected, the output was:

Code:

Regards,

Paramesh.

netnut · #4 17-Dec-2005, 09:37

Thanx for the tip Paramesh, I didn't know that...., maybe I thought that compuetrs these days have that much of IQ to handle numbers beginning with a zero.
Jokes apart, suppose at runtime a user enters a number beginning with a zero would the compiler take it as a hex/oct number? Then how can I "decode" them are there any standard library features to use or do i need to develop my own code (P.s. I use Turbo C++ 3.0)

lian1238 · #5 12-Jan-2006, 02:54

if you need to use before numbers, use a double. right?

lian1238 · #6 12-Jan-2006, 02:56

if you need to use 0 before numbers, use double instead of int.

UMLseek · #7 11-Feb-2007, 00:46

Quote:

Originally Posted by Paramesh

Language: C/C++
Level: Beginner

Dont use 0 before numbers.
Instead of using 010, use 10.

For example consider this example:

CPP / C++ / C Code:

 #include<stdio.h>
 int main() {
     int a[8] = { 000, 001, 010, 011, 100, 101, 110, 111 };
     int i;
     for(i = 0; i < 8; i++ ) {
         printf("%d\n", a[i]);
     }
     return 0;
 }

Expected output:

Code:

Actual Output:

Code:

Because Numbers that start with 0 are taken as Octal, so 010 is taken as 10-octal or 8-decimal.

So, we should be careful in using numbers.

Another example:

CPP / C++ / C Code:

 #include<stdio.h>
 int main() {
     int a[8] = { 0000, 0001, 0010, 0011, 0100, 0101, 0110, 0111 };
     int i;
     for(i = 0; i < 8; i++ ) {
         printf("%d\n", a[i]);
     }
     return 0;
 }

As expected, the output was:

Code:

Regards,

Paramesh.

Paramesh,
You English borders on to flawless. How come?
You command over the basics is so refreshing. Keep up the good work.

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