My sister needs to know

[swgh]

Hi, no, she doesnt want a date! She is learning C, ( I do C++ )

anyway, the question she asks comes from a text book. The sample code it has I have placed below with the comment from the book included. She wants to know why in C++ you can have the control variable inside a for loop and in C it must be declared outside. i personally think it has somthing to do when they changed the standard in C++, but I could be wrong..

Here is the code, what is the reason? read the comment in the code for a better understanding!

#include <stdio.h>

int main()
{
int i;   /* in C, you MUST  declare the control variable outside the 
              loop. This is not the case in C++, where control variables
              can be initalized inside the loop */

for ( i = 0; i <= 10; i++ )
{
printf("%d", i);
}

getchar();

return 0;
}

[Ancient Dragon]

In C, all variables must be declared at the top of the bloci in which it is to be used and a for loop does not start the top of the block -- braces '{' do that. In c++ variables can be declared anywhere but always before they are used. And an integer declared in the for loop has scope only within that for loop.

C++ didn't change the standard. C and C++ each have their own ISO standards.

[Salem]

Perhaps she should join the board and ask her own questions on the C board.

[okinrus]

Hi, no, she doesnt want a date! She is learning C, ( I do C++ )

anyway, the question she asks comes from a text book. The sample code it has I have placed below with the comment from the book included. She wants to know why in C++ you can have the control variable inside a for loop and in C it must be declared outside. i personally think it has somthing to do when they changed the standard in C++, but I could be wrong..

Here is the code, what is the reason? read the comment in the code for a better understanding!

In C++, objects are sometimes constructed in the middle function. Their initialization occurs in the constructor. For example, you could have

void f()
{
        int c = 4 + 4;

        for (int i = 0; i < 10; ++i)
               c++;

       Person person(c);
}

The construction of the object person must occur after c is processed. If C++ didn't allow construction in the middle, then you'd have to write

void f()
{
        int c = 4 + 4;
        Person person;

        for (int i = 0; i < 10; ++i)
               c++;

       person.init(c);
}

This results in a useless constructor with some objects uninitialized. C++ tries to enforce the rule that every object is initialized and no method is called on the object until the object is initialized. This rule reduces errors because calling a method on an unitialized object is almost always an error.