I am learning C++ for the first time. I have no previous programming background.
In the book I have I saw this example.
#include <iostream>
using::cout;
using::endl;
int main()
{
int x = 5;
char y = char(x);
cout << x << endl;
cout << y << endl;
return 0;
}
The example makes sense: print an integer and the ASCII representation of it.
Now, I created a text file with these values.
48
49
50
51
55
56
75
I am writing a program to read this text file -- "theFile.txt" -- and want to convert these numbers to the ASCII value.
Here is the code I wrote.
#include <iostream>
#include <fstream>
using std::cout;
using std::endl;
using std::ifstream;
int main()
{
ifstream thestream;
thestream.open("theFile.txt");
char thecharacter;
while (thestream.get(thecharacter))
{
int theinteger = int(thecharacter);
char thechar = char(theinteger);
cout << theinteger << "\t" << thechar << endl;
}
system ("PAUSE");
return 0;
}
This is my understanding about the second program shown.
The compiler does not know the exact data type that is contained in "theFile.txt". As a result, I need to specify it so I choose to read the data as a char.
I read the each digit in the file as a char and converted it to an integer value and stored it in "theinteger".
Since I have an integer in "theinteger" I want to print it out as a character but char thechar = char(theinteger); does not work as intended.
What am I doing incorrect?
You are reading char by char, but you really (I think) want to read each sequence of digits as an integer. Change your loop to:
int theinteger;
while (thestream >> theinteger )
{
char thechar = char(theinteger);
cout << thechar << endl;
}
+1 For a very nicely formatted & expressed first question, BTW!
You are reading one char at a time from the file. Hence, if your file contains:
2424
You will first read the char "2" from the file, convert it to an int, and then back to a char, which will print "2" on cout. Next round will print "4", and so on.
If you want to read the numbers as full numbers, you need to do something like:
int theinteger;
thestream >> theinteger;
cout << char(theinteger) << endl;
Related
I am working on below code:
#include<iostream>
#include<stdio.h>
using namespace std;
main() {
unsigned char a;
a=1;
printf("%d", a);
cout<<a;
}
It is printing 1 and some garbage.
Why cout is behaving so?
cout << a is printing a value which appears to be garbage to you. It is not garbage actually. It is just a non-printable ASCII character which is getting printed anyway. Note that ASCII character corresponding to 1 is non-printable. You can check whether a is printable or not using, std::isprint as:
std::cout << std::isprint(a) << std::endl;
It will print 0 (read: false) indicating the character is non-printable
--
Anyway, if you want your cout to print 1 also, then cast a to this:
cout << static_cast<unsigned>(a) << std::endl;
I had a similar issue here that I've long forgotten about. The resolution to this problem with iostream's cout can be done like this:
#include<iostream>
#include<stdio.h>
main() {
unsigned char a;
a=1;
printf("%d", a);
std::cout<< +a << std::endl;
return 0;
}
instead of casting it back to another type if you want cout to print the unsigned char value as opposed to the ascii character. You need to promote it.
If you noticed all I did was add a + before the unsigned char. This is unary addition that will promote the unsigned char to give you the actual number representation.
User Baum mit Augen is responsible for reminding me of this solution.
You need to typecast a as integer as cout<< (int)(a);. With this you will observe 1 on the output. With cout << a;, the print will be SOH (Start of Heading) corresponding to ascii value of 1 which can't be printed and hence, some special character is observed.
EDIT:
To be more accurate, the cout statement should be cout << static_cast<unsigned>(a) as Nawaz has mentioned.
The C compiler has its own way of defining the type of the printed output, because you can specify the type of the output.
Ex:
uint8_t c = 100;
printf("%d",c);
so you can also print c as an int by %d, or char %c, string %s or a hex value %x.
Where C++ has its own way too, the cout prints the 8-bit values as a char by default. So, you have to use specifiers with the output argument.
You can either use:
a + before the name of the output argument
uint8_t data_byte = 100;
cout << "val: " << +data_byte << endl;
use a function cast unsigned(var); like,
uint8_t data_byte = 100;
cout << "val: " << unsigned(data_byte) << endl;
printf("%u",a);
its so simple try it
The code asks for a positive integer, than the first output shows the corresponding ASCII code, the others are made to convert the integer to decimal, octal and hexadecimal equivalents. I understand the logic of the code, but I don't understand the assignment made on line 10 c=code than the assignment made on line 12 code=c. What happens on background when we 'swap' the two variables.
#include <iostream>
#include <iomanip>
using namespace std;
int main(){
unsigned char c = 0;
unsigned int code = 0;
cout << "\nPlease enter a decimal character code: ";
cin >> code;
c = code;
cout << "\nThe corresponding character: " << c << endl;
code = c;
cout << "\nCharacter codes"
<< "\n decimal: " << setw(3) << dec << code
<< "\n octal: " << setw(3) << oct << code
<< "\n hexadecimal: " << setw(3) << hex << code
<< endl;
return 0;
}
I could be wrong here so maybe someone else can weigh in, but I believe I know the answer.
If you assign a character a number, when you print that char it prints the corresponding character. Since c is of type char, the line c = code converts the integer entered into a character. You can test this yourself by assigning any int to a char variable and printing it out.
The second assignment, code = c, seems to be completely unnecessary.
That's not a swap. c is assigned the same value as code and then this value is assigned back to code. The original value of code is lost.
We can see this because unsigned char c is (usually) much smaller than unsigned int code and some information may be lost stuffing the value in code into c.
For example, code = 257. After c = code; code is still 257 and c, assuming an 8 bit char will be 1. After code = c;, both code and c will be 1. 257 has been lost.
Why is this being done? when given a char, operator<< will print out the character encoded, completely ignoring the request to print as hex, dec, or oct. So
<< "\n decimal: " << setw(3) << dec << c
is wasted. Given an int << will respect the modifiers, but if c and code have different values, you're comparing apples and Sasquatches.
int main()
{
char hmm[1000];
cin.getline(hmm, 1000);
cout << hmm << endl; //this was to test if I could assign my input to the array properly
for (int sayac = 0; hmm[sayac] != '#'; sayac++) {
if (!isdigit(hmm[sayac])) {
if (islower(hmm[sayac]))
cout << toupper(hmm[sayac]);
else if (isupper(hmm[sayac]))
cout << tolower(hmm[sayac]);
else
cout << hmm[sayac];
}
}
"Write a program that reads keyboard input to the # symbol and that echoes the input
except for digits, converting each uppercase character to lowercase, and vice versa.
(Don’t forget the cctype family.) "
I'm doing this exercise from the primer book. But when I run it, it returns the ascii order of the char, not the uppercase/lowercase version of the character. Couldn't figure out the problem. Can someone tell my why please?
(I may have other problems about the exercise, please don't correct them if I have. I want to fix it on my own (except the problem I explained), but I can't check the other ones as I have this problem.
When writing
std::cout << toupper('a');
the following happen:
int toupper(int ch) is called, and returns an integer whose value is 'A' (0x41).
std::basic_ostream::operator<<(std::cout, 0x41) is called, that is the int (2) overload since an int was provided.
Overall, it prints "65".
As a solution, you can cast back your upper case to a char:
std::cout << static_cast<char>(toupper('a'));
It's a question of representation. There is no difference between a character and that character's numeric value. It's all in how you choose to display it. For example, the character 'a' is just a constant with a value equal to the character's numeric value.
The problem you are having is that std::toupper and std::tolower return an int rather than a char. One reason for that is that they handle EOF values, which are not necessarily representable by char. As a consequence, std::cout see you are trying to print an int and not a char. The standard behavior for streaming an int is to print the number. The solution is then to cast your result to char to force the value to be interpreted as a character. You can use something like std::cout << static_cast<char>(std::toupper(hmm[sayac]));.
Try the following :
#include <cctype>
#include <iostream>
int main()
{
char hmm[1000];
std::cin.getline(hmm, 1000);
std::cout << hmm << std::endl; //this was to test if I could assign my input to the array properly
for (int sayac = 0; hmm[sayac] != '#'; sayac++) {
if (!std::isdigit(hmm[sayac])) {
if (std::islower(hmm[sayac]))
std::cout << static_cast<char>(std::toupper(hmm[sayac]));
else if (isupper(hmm[sayac]))
std::cout << static_cast<char>(std::tolower(hmm[sayac]));
else
std::cout << hmm[sayac];
}
}
}
You should also consider using an std::string instead of an array of char of arbitrary length. Also, take note that you have undefined behavior if the input string does not contain #.
I am a high school beginner to C++ (Less than 1 month since I started). I have been trying to convert a int into its char value. (So, a 5 should convert to a '5')
I am aware how to convert from char to int (from '5' to 5), by subtracting 48 from it, however I am unable to cast the other way. Here's what I tried:
#include <iostream>
using namespace std;
int main()
{
int x = 5;
cout<<x<<endl;
cout<<(char)x<<endl;
cout<<static_cast<char>(x)<<endl;
cout<<"end of program"<<endl;
}
The output I get is
5
end of program
I am unsure why I don't get an output. Appreciate any advice.
The cast is working perfectly fine (for what you're doing).
You're casting a 5 to it's ASCII value. Look at an ASCII table and see what a 5 represents.
Now for what you're trying to do, try cout << (char)(x+48) << endl;
Try the following
#include <iostream>
using namespace std;
int main()
{
int x = 5;
cout << x << endl;
cout << ( char )( x + '0' ) << endl;
cout << static_cast<char>( x + '0' ) < <endl;
cout << "end of program" < <endl;
}
And you have not to look through ASCII table.:) Take into account that there is EBCDIC table. The code I showed does not depend on a coding table. The C++ Standard guarantees that all characters of digits follow each other starting from '0' to '9'.
I am working on below code:
#include<iostream>
#include<stdio.h>
using namespace std;
main() {
unsigned char a;
a=1;
printf("%d", a);
cout<<a;
}
It is printing 1 and some garbage.
Why cout is behaving so?
cout << a is printing a value which appears to be garbage to you. It is not garbage actually. It is just a non-printable ASCII character which is getting printed anyway. Note that ASCII character corresponding to 1 is non-printable. You can check whether a is printable or not using, std::isprint as:
std::cout << std::isprint(a) << std::endl;
It will print 0 (read: false) indicating the character is non-printable
--
Anyway, if you want your cout to print 1 also, then cast a to this:
cout << static_cast<unsigned>(a) << std::endl;
I had a similar issue here that I've long forgotten about. The resolution to this problem with iostream's cout can be done like this:
#include<iostream>
#include<stdio.h>
main() {
unsigned char a;
a=1;
printf("%d", a);
std::cout<< +a << std::endl;
return 0;
}
instead of casting it back to another type if you want cout to print the unsigned char value as opposed to the ascii character. You need to promote it.
If you noticed all I did was add a + before the unsigned char. This is unary addition that will promote the unsigned char to give you the actual number representation.
User Baum mit Augen is responsible for reminding me of this solution.
You need to typecast a as integer as cout<< (int)(a);. With this you will observe 1 on the output. With cout << a;, the print will be SOH (Start of Heading) corresponding to ascii value of 1 which can't be printed and hence, some special character is observed.
EDIT:
To be more accurate, the cout statement should be cout << static_cast<unsigned>(a) as Nawaz has mentioned.
The C compiler has its own way of defining the type of the printed output, because you can specify the type of the output.
Ex:
uint8_t c = 100;
printf("%d",c);
so you can also print c as an int by %d, or char %c, string %s or a hex value %x.
Where C++ has its own way too, the cout prints the 8-bit values as a char by default. So, you have to use specifiers with the output argument.
You can either use:
a + before the name of the output argument
uint8_t data_byte = 100;
cout << "val: " << +data_byte << endl;
use a function cast unsigned(var); like,
uint8_t data_byte = 100;
cout << "val: " << unsigned(data_byte) << endl;
printf("%u",a);
its so simple try it