Type Casting
I'm having a problem in understanding the difference when we type cast a variable from char to int and from char to double/float... is there any difference at all between the 2??????
You'll need to be a bit more specific, as there are a couple different types of casting. If you're not sure, you could give a code example.
Here's a code wherein both an int and a float having the values 65 are being tpe casted to a char value and the result's same in both cases.....
#include<conio.h>
#include<iostream.h>
void main()
{
clrscr();
char c_1,c_2;
int i=65;
float f=65.0;
c_1=char(i);
c_2=char(f);
cout<<"Type Casted Int=: "<<c_1<<endl<<"Type Casted Float=: "<<c_2;
getch();
}
#include<conio.h>
#include<iostream.h>
void main()
{
clrscr();
char c_1,c_2;
int i=65;
float f=65.0;
c_1=char(i);
c_2=char(f);
cout<<"Type Casted Int=: "<<c_1<<endl<<"Type Casted Float=: "<<c_2;
getch();
}
Now here's a code wherein 2 char variables having the same value 'A' are being type casted seperately into int and float and still the result remains same.......
#include<conio.h>
#include<iostream.h>
void main()
{
clrscr();
char c_1='A',c_2='A';
int i;
float f;
i=int(c_1);
f=float(c_2);
cout<<"Int=: "<<c_1<<endl<<"Float=: "<<c_2;
getch();
}
my question is why is the result the same in both cases???? Does that mean that type conversion from char to any other data type would remain same in all the cases????????
#include<conio.h>
#include<iostream.h>
void main()
{
clrscr();
char c_1='A',c_2='A';
int i;
float f;
i=int(c_1);
f=float(c_2);
cout<<"Int=: "<<c_1<<endl<<"Float=: "<<c_2;
getch();
}
my question is why is the result the same in both cases???? Does that mean that type conversion from char to any other data type would remain same in all the cases????????
replace
cout<<"Int=: "<<c_1<<endl<<"Float=: "<<c_2;
with
cout << "Int=: "<< i << "\nFloat=: " << f;
cout<<"Int=: "<<c_1<<endl<<"Float=: "<<c_2;
with
cout << "Int=: "<< i << "\nFloat=: " << f;
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A char essentially contains one byte of data. Floats and ints contain four bytes.
When going from an int to a char the value might get cut off since chars can only store the values (-128,+127).
e.g. Let's take a (signed) integer, n = 1000, such that in C++ code
n is represented internally as:
where the top numbers represent the bit position (from left to right decreasing in significance). Bit 31 is the sign bit (0 means positive or no sign and 1 means negative). You can see through calculation that:
In C++, if you were to do
After the cast, c would store:
You can see that these are bits 0-7 of n. If c were to be cast back to an int, the int would store the value -24 (because c is a signed char storing the possible values (-128,+127) in two's complement).
To see how we get -24 from the above binary representation, we do the following. Since there is a 1 in the most significant bit, we know the number is negative. To find the absolute value of the decimal representation, we flip the ones and zeroes:
and add 1:
which gives us the number 24, so the original two's complement number is -24.
If, on the other hand, the sign bit was not on, i.e. if c stored the following:
which means that n would have been 872 (1000 - 128), then if c were to be cast back to an int, then the int would store the value 104. This is as expected because
To summarize what we have so far, if we're dealing with (signed)
From my experimentation, I've found that float values are truncated and treated as an integer if cast into a char. Therefore, c and c2 would have the same value in the code below.
If c and c2 were then cast to ints, both ints would have the decimal value 65. Note that no cut-off happens if you place any number between (-128,+127) into a char. The above explains why you're getting the same values in your first example.
Floats have different binary representations (sign, exponent, mantissa), however, when casting from a char to a float, the value of the char (in two's complement) would be placed into the float just as the value of the char would be placed into an int. That is why in your second example both
I would venture a guess that conversion from char to other basic data types would be the same (i.e. determine its decimal value (from two's complement) and copy that value into the variable).
When going from an int to a char the value might get cut off since chars can only store the values (-128,+127).
e.g. Let's take a (signed) integer, n = 1000, such that in C++ code
int n = 1000;n is represented internally as:
|
|
where the top numbers represent the bit position (from left to right decreasing in significance). Bit 31 is the sign bit (0 means positive or no sign and 1 means negative). You can see through calculation that:
|
|
In C++, if you were to do
char c = char(n);, what would happen is it would take the least significant byte of n and put it into c.After the cast, c would store:
|
|
You can see that these are bits 0-7 of n. If c were to be cast back to an int, the int would store the value -24 (because c is a signed char storing the possible values (-128,+127) in two's complement).
To see how we get -24 from the above binary representation, we do the following. Since there is a 1 in the most significant bit, we know the number is negative. To find the absolute value of the decimal representation, we flip the ones and zeroes:
|
|
and add 1:
|
|
which gives us the number 24, so the original two's complement number is -24.
If, on the other hand, the sign bit was not on, i.e. if c stored the following:
|
|
which means that n would have been 872 (1000 - 128), then if c were to be cast back to an int, then the int would store the value 104. This is as expected because
|
|
To summarize what we have so far, if we're dealing with (signed)
chars and (signed) ints:| 1. Conversion from an int to a char involves putting the least significant byte into the char. 2. Conversion from a char to an int involves determining the char's decimal representation from two's complement |
From my experimentation, I've found that float values are truncated and treated as an integer if cast into a char. Therefore, c and c2 would have the same value in the code below.
|
|
If c and c2 were then cast to ints, both ints would have the decimal value 65. Note that no cut-off happens if you place any number between (-128,+127) into a char. The above explains why you're getting the same values in your first example.
Floats have different binary representations (sign, exponent, mantissa), however, when casting from a char to a float, the value of the char (in two's complement) would be placed into the float just as the value of the char would be placed into an int. That is why in your second example both
i and f have the same values (even though in your example you printed the characters and not the numerical values).I would venture a guess that conversion from char to other basic data types would be the same (i.e. determine its decimal value (from two's complement) and copy that value into the variable).
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