C++ manipulating numbers in ASCII to stay only in range of letters - c++

#include <iostream>
using namespace std;
Int main() {
cout<<"Give me a letter" <<endl;
char letter;
cin>>letter;
cout<<letter;
(Int)letter;
letter+=2;
cout<<(char)letter;
(Int)letter;
letter-=25;
cout<<(char)letter;
return 0;
}
How would I manipulate the numbers in a way so that the numbers will always output a letter.
ie: if the letter z was chosen and adding 2 is a symbol how would I manipulate it in a way so that it will always stay between the numbers for capital numbers and uncapitalized numbers. Thanks. Please try to keep answers at a beginner level please I am new to this.

if(letter > 'z') {
//do stuff
}
if(letter < 'a' && letter > 'Z') {
//do stuff
}
if(letter < 'A') {
//do stuff
}
It just depends on how you want to handle the character when it goes into one of the three ranges on the ASCII chart in which the characters are not letters.
As a side note, you don't have to cast a char to an int to do math with it.
char myChar = 'a' + 2;
cout << myChar;
This will print: c
c has an ASCII value of 2 more than a.

The surest method is to use a table for each category, and do
your arithmetic on its index, modulo the size of the table.
Thus, for just lower case letters, you might do something like:
char
transcode( char original )
{
char results = original;
static std::string const lower( "abcdefghijklmnopqrstuvwxyz" );
auto pos = std::find( lower.begin(), lower.end(), results );
if ( pos != lower.end() ) {
int index = pos - lower.begin();
index = (index + 2) % lower.size();
results = lower[ index ];
}
return results;
}
This solution is general, and will work regardless of the sets
of letters you want to deal with. For digits (and for upper and
lower case, if you aren't too worried about portability), you
can take advantage of the fact that the code points are
contiguous, and do something like:
char
transcode( char original )
{
char results = original;
if ( results >= '0' && results <= '9' ) {
char tmp = results - '0'
tmp = (tmp + 2) % 10;
results = tmp + '0';
}
return results;
}
An alternative implementation would be to use something like:
results = results + 2;
if ( results > '9' ) {
results -= 10;
}
in the if above. These two solutions are mathematically
equivalent.
This is only guaranteed to work for digits, but will generally
work for upper or lower case if you limit yourself to the
original ASCII character set. (Be aware that most systems today
support extended character sets.)

You can test directly against ASCII chars by using 'x' notation. Further, you can test things together using && ("and" respectively"):
if ('a' <= letter && letter <= 'z') {
// Letter is between 'a' and 'z'
} else if ('A' <= letter && letter <= 'Z')) {
// Letter is between 'A' and 'Z'
} else {
// Error! Letter is not between 'a' and 'z' or 'A' and 'Z'
}
Or you can use the standard library function std::isalpha which handles this for you:
if (std::isalpha(letter)) {
// Letter is between 'a' and 'z' or 'A' and 'Z'
} else {
// Error! Letter is not between 'a' and 'z' or 'A' and 'Z'
}

Related

How to store in a string and convert to character array?

Write a C++ program to perform addition of two hexadecimal numerals which are less than 100 digits long. Use arrays to store hexadecimal numerals as arrays of characters.the solution is to add the corresponding digits in the format of hexadecimal directly. From right to left, add one to the digit on the left if the sum of the current digits exceed 16. You should be able to handle the case when two numbers have different digits.
The correct way to get the input is to store as character array. You can either first store in a string and convert to character array, or you can use methods such as cin.getline(), getc(), cin.get() to read in the characters.
I don't know what is wrong with my program and it I don't know how to use the function getline() and eof()
char a[number1],b[number1],c[number2],h;
int m,n,p(0),q(0),k,d[number1],z[number1],s[number2],L,M;
cout<<"Input two hexadecimal numerals(both of them within 100 digits):\n";
cin.getline(a,100);
cin.getline(b,100);
int x=strlen(a) ;
int y=strlen(b);
for(int i=0;i<(x/2);i++)
{
m=x-1-i;
h=a[i];
a[i]=a[m];
a[m]=h;
}
for(int j=0;j<(y/2);j++)
{
n=y-1-j;
h=b[j];
b[j]=b[n];
b[n]=h;
}
if(x>y)
{
for(int o=0;o<x;o++)//calculate a add b
{
if(o>=(y-1))
z[o]=0;//let array b(with no character)=0
if(a[o]=='A')
d[o]=10;
else if(a[o]=='B')
d[o]=11;
else if(a[o]=='C')
d[o]=12;
else if(a[o]=='D')
d[o]=13;
else if(a[o]=='E')
d[o]=14;
else if(a[o]=='F')
d[o]=15;
else if(a[o]=='0')
d[o]=0;
else if(a[o]=='1')
d[o]=1;
else if(a[o]=='2')
d[o]=2;
else if(a[o]=='3')
d[o]=3;
else if(a[o]=='4')
d[o]=4;
else if(a[o]=='5')
d[o]=5;
else if(a[o]=='6')
d[o]=6;
else if(a[o]=='7')
d[o]=7;
else if(a[o]=='8')
d[o]=8;
else if(a[o]=='9')
d[o]=9;
if(b[o]=='A')
z[o]=10;
else if(b[o]=='B')
z[o]=11;
else if(b[o]=='C')
z[o]=12;
else if(b[o]=='D')
z[o]=13;
else if(b[o]=='E')
z[o]=14;
else if(b[o]=='F')
z[o]=15;
else if(b[o]=='0')
z[o]=0;
else if(b[o]=='1')
z[o]=1;
else if(b[o]=='2')
z[o]=2;
else if(b[o]=='3')
z[o]=3;
else if(b[o]=='4')
z[o]=4;
else if(b[o]=='5')
z[o]=5;
else if(b[o]=='6')
z[o]=6;
else if(b[o]=='7')
z[o]=7;
else if(b[o]=='8')
z[o]=8;
else if(b[o]=='9')
z[o]=9;
p=d[o]+z[o]+q;
if(p>=16)//p is the remained number
{
q=1;
p=p%16;
}
else
q=0;
if(p==0)
c[o]='0';
else if(p==1)
c[o]='1';
else if(p==2)
c[o]='2';
else if(p==3)
c[o]='3';
else if(p==4)
c[o]='4';
else if(p==5)
c[o]='5';
else if(p==6)
c[o]='6';
else if(p==7)
c[o]='7';
else if(p==8)
c[o]='8';
else if(p==9)
c[o]='9';
else if(p==10)
c[o]='A';
else if(p==11)
c[o]='B';
else if(p==12)
c[o]='C';
else if(p==13)
c[o]='D';
else if(p==14)
c[o]='E';
else if(p==15)
c[o]='F';
}
k=x+1;
if(q==1)//calculate c[k]
{
c[k]='1';
for(int f=0;f<=(k/2);f++)
{
m=k-f;
h=c[f];
c[f]=c[m];
c[m]=h;
}
}
else
{
for(int e=0;e<=(x/2);e++)
{
m=x-e;
h=c[e];
c[e]=c[m];
c[m]=h;
}
}
}
if(x=y)
{
for(int o=0;o<x;o++)//calculate a add b
{
if(a[o]=='A')
d[o]=10;
else if(a[o]=='B')
d[o]=11;
else if(a[o]=='C')
d[o]=12;
else if(a[o]=='D')
d[o]=13;
else if(a[o]=='E')
d[o]=14;
else if(a[o]=='F')
d[o]=15;
else if(a[o]=='0')
d[o]=0;
else if(a[o]=='1')
d[o]=1;
else if(a[o]=='2')
d[o]=2;
else if(a[o]=='3')
d[o]=3;
else if(a[o]=='4')
d[o]=4;
else if(a[o]=='5')
d[o]=5;
else if(a[o]=='6')
d[o]=6;
else if(a[o]=='7')
d[o]=7;
else if(a[o]=='8')
d[o]=8;
else if(a[o]=='9')
d[o]=9;
if(b[o]=='A')
z[o]=10;
else if(b[o]=='B')
z[o]=11;
else if(b[o]=='C')
z[o]=12;
else if(b[o]=='D')
z[o]=13;
else if(b[o]=='E')
z[o]=14;
else if(b[o]=='F')
z[o]=15;
else if(b[o]=='0')
z[o]=0;
else if(b[o]=='1')
z[o]=1;
else if(b[o]=='2')
z[o]=2;
else if(b[o]=='3')
z[o]=3;
else if(b[o]=='4')
z[o]=4;
else if(b[o]=='5')
z[o]=5;
else if(b[o]=='6')
z[o]=6;
else if(b[o]=='7')
z[o]=7;
else if(b[o]=='8')
z[o]=8;
else if(b[o]=='9')
z[o]=9;
p=d[o]+z[o]+q;
M=p;
if(p>=16)
{
q=1;
p=p%16;
}
else
q=0;
s[o]=p;
if(p==0)
c[o]='0';
else if(p==1)
c[o]='1';
else if(p==2)
c[o]='2';
else if(p==3)
c[o]='3';
else if(p==4)
c[o]='4';
else if(p==5)
c[o]='5';
else if(p==6)
c[o]='6';
else if(p==7)
c[o]='7';
else if(p==8)
c[o]='8';
else if(p==9)
c[o]='9';
else if(p==10)
c[o]='A';
else if(p==11)
c[o]='B';
else if(p==12)
c[o]='C';
else if(p==13)
c[o]='D';
else if(p==14)
c[o]='E';
else if(p==15)
c[o]='F';
}
k=x+1;
if(q==1)
{
c[k]='1';
for(int f=0;f<=(k/2);f++)
{
m=k-f;
h=c[f];
c[f]=c[m];
c[m]=h;
}
}
else
{
for(int e=0;e<=(x/2);e++)
{
m=x-e;
h=c[e];
c[e]=c[m];
c[m]=h;
}
}
}
Lets look at what cin.getline does:
Extracts characters from stream until end of line. After constructing
and checking the sentry object, extracts characters from *this and
stores them in successive locations of the array whose first element
is pointed to by s, until any of the following occurs (tested in the
order shown):
end of file condition occurs in the input sequence (in which case setstate(eofbit) is executed)
the next available character c is the delimiter, as determined by Traits::eq(c, delim). The delimiter is extracted (unlike basic_istream::get()) and counted towards gcount(), but is not stored.
count-1 characters have been extracted (in which case setstate(failbit) is executed).
If the function extracts no characters (e.g. if count < 1), setstate(failbit)
is executed. In any case, if count>0, it then stores a null character
CharT() into the next successive location of the array and updates
gcount().
The result of that is in all cases, s now points to a null terminated string, of at most count-1 characters.
In your usage, you have up to 99 digits, and can use strlen to count exactly how many. eof is not a character, nor it is a member function of char.
You then reverse in place the inputs, and go about your overly repetitious conversions.
However, it's much simpler to use functions, both those you write yourself and those provided by the standard.
// translate from '0' - '9', 'A' - 'F', 'a' - 'f' to 0 - 15
static std::map<char, int> hexToDec { { '0', 0 }, { '1', 1 }, ... { 'f', 15 }, { 'F', 15 } };
// translate from 0 - 15 to '0' - '9', 'A' - 'F'
static std::map<int, char> decToHex { { 0, '0' }, { 1, '1' }, ... { 15, 'F' } };
std::pair<char, bool> hex_add(char left, char right, bool carry)
{
// translate each hex "digit" and add them
int sum = hexToDec[left] + hexToDec[right];
// we have a carry from the previous sum
if (carry) { ++sum; }
// translate back to hex, and check if carry
return std::make_pair(decToHex[sum % 16], sum >= 16);
}
int main()
{
std::cout << "Input two hexadecimal numerals(both of them within 100 digits):\n";
// read two strings
std::string first, second;
std::cin >> first >> second;
// reserve enough for final carry
std::string reverse_result(std::max(first.size(), second.size()) + 1, '\0');
// traverse the strings in reverse
std::string::const_reverse_iterator fit = first.rbegin();
std::string::const_reverse_iterator sit = second.rbegin();
std::string::iterator rit = reverse_result.begin();
bool carry = false;
// while there are letters in both inputs, add (with carry) from both
for (; (fit != first.rend()) && (sit != second.rend()); ++fit, ++sit, ++rit)
{
std::tie(*rit, carry) = hex_add(*fit, *sit, carry);
}
// now add the remaining digits of first (will do nothing if second is longer)
for (; (fit != first.rend()); ++fit)
{
// we need to account for a carry in the last place
// potentially all the way up if we are adding e.g. "FFFF" to "1"
std::tie(*rit, carry) = hex_add(*fit, *rit++, carry);
}
// or add the remaining digits of second
for (; (sit != second.rend()); ++sit)
{
// we need to account for a carry in the last place
// potentially all the way up if we are adding e.g. "FFFF" to "1"
std::tie(*rit, carry) = hex_add(*sit, *rit++, carry);
}
// result has been assembled in reverse, so output it reversed
std::cout << reverse_result.reverse();
}
Regarding the text of your problem: “add one to the digit on the left if the sum of the current digits exceed 16” is wrong; it should be 15, not 16.
Regarding your code: I did not have the patience to read all your code, however:
I have noticed one long if/else. Use a switch (but you do not need one).
To find out if a character is a hex digit use isxdigit (#include <cctype>).
The user might input uppercase and lowercase characters: convert them to the same case using toupper/tolower.
To convert a hex digit to an integer:
if the digit is between ‘0’ and ‘9’ simply subtract ‘0’. This works because the codes for ‘0’, ‘1’… are 0x30, 0x31... (google ASCII codes).
if the digit is between ‘A’ and ‘F’, subtract ‘A’ and add 10.
Solving the problem:
“less than 100 digits long” This is a clear indication regarding how your data must be stored: a simple 100 long array, no std::string, no std::vector:
#define MAX_DIGITS 100
typedef int long_hex_t[MAX_DIGITS];
In other words your numbers are 100 digits wide, at most.
Decide how you store the number: least significant digit first or last? I would chose to store the least significant first. 123 is stored as {3,2,1,0,…0}
Use functions to simplify your code. You will need three functions: read, print and add:
int main()
{
long_hex_t a;
read( a );
long_hex_t b;
read( b );
long_hex_t c;
add( c, a, b );
print( c );
return 0;
}
The easiest function to write is add followed by print and read.
For read use get and putback to analyze the input stream: get extracts the next character from stream and putback is inserting it back in stream (if we do not know how to handle it).
Here it is a full solution (try it):
#include <iostream>
#include <cctype>
#define MAX_DIGITS 100
typedef int long_hex_t[MAX_DIGITS];
void add( long_hex_t c, long_hex_t a, long_hex_t b )
{
int carry = 0;
for ( int i = 0; i < MAX_DIGITS; ++i )
{
int t = a[i] + b[i] + carry;
c[i] = t % 16;
carry = t / 16;
}
}
void print( long_hex_t h )
{
//
int i;
// skip leading zeros
for ( i = MAX_DIGITS - 1; i >= 0 && h[i] == 0; --i )
;
// all zero
if ( i < 0 )
{
std::cout << '0';
return;
}
// print remaining digits
for ( i; i >= 0; --i )
std::cout << char( h[i] < 10 ? h[i] + '0' : h[i] - 10 + 'A' );
}
void read( long_hex_t h )
{
// skip ws
std::ws( std::cin );
// skip zeros
{
char c;
while ( std::cin.get( c ) && c == '0' )
;
std::cin.putback( c );
}
//
int count;
{
int i;
for ( i = 0; i < MAX_DIGITS; ++i )
{
char c;
if ( !std::cin.get( c ) )
break;
if ( !std::isxdigit( c ) )
{
std::cin.putback( c );
break;
}
c = std::toupper( c );
h[i] = c <= '9'
? ( c - '0' )
: ( c - 'A' + 10 );
}
count = i;
}
// reverse
for ( int i = 0, ri = count - 1; i < count / 2; ++i, --ri )
{
int t = h[i];
h[i] = h[ri];
h[ri] = t;
}
// fill the rest with zero
for ( int i = count; i < MAX_DIGITS; ++i )
h[i] = 0;
}
int main()
{
long_hex_t a;
read( a );
long_hex_t b;
read( b );
long_hex_t c;
add( c, a, b );
print( c );
return 0;
}
This is a long answer. Because you have much bug in your code. Your using of getline is ok. But your are calling a eof() like e.eof() which is wrong. If you have looked at your compilation error, you would see that it was complaining about calling eof() on the variable e because it is of non-class type. Simple meaning it is not an object of some class. You cannot put the dot operator . on primitive types like that. I think what you are wanting to do, is to terminate the loop when you have reached the end of line. So that index1 and index2 can get the length of the string input. If I were you, I would just use C++ builtin strlen() function for that. And in the first place, you should use C++ class string to handle strings. Also strings have a null - terminating character '\0' at the end of them. If you don't know about it, I suggest you take some time to read about strings.
Secondly, you have many bugs and errors in your code. The way you are reversing your string is not correct. Ask yourself, what are the contents of the arrays a and b at position which have higher index than the length of the string? You should use reverse() for reversing strings and arrays.
You have errors on adding loop also. Note, you are changing the arrays value when they are A, B, C, D, and so on for hexadecimal values with the corresponding decimal values 10,11,12,13 and so on. But you should change the values for the character '0' - '9' also. Because when the array holds '0' it is not integer 0. But is is ASCII '0' which has integer value of 48. And the character '1' has integer value of 49 and so on. You want to replace this values with corresponding integer values also. When you are also storing the result values in c, you are only handling only those values which are above 9 and replacing them with corresponding characters. You should also replace the integers 0 - 9 with there corresponding ASCII characters. Also don't forget to put a null terminating character at the end of the result.
Also, when p is getting larger than 15, you are only changing your carry, but you should also change p accordingly.
I believe you can reverse the result array c in a much more elegant way. By only reversing when the calculation has been performed totally. You can simple call reverse() for that.
I believe you can think hard a little bit more, and write the code in the right way. I have a few suggestions for you, don't use variable names like a,b,c,o. Try to name variables with what are they really doing. Also, you can improve your algorithm and shorten your code and headache with one simple change in the algorithm. First find the length of a and then find the length of b. If there lengths are unequal, find out which has lesser length. Then add 0s in front of it to make both lengths equal. Now, you can simply start from the back, and perform the addition. Also, you should use builtin methods like reverse() , swap() and also string class to make your life easier ;)
#include <iostream>
#include <algorithm>
#include <string>
using namespace std;
int main(){
string firstVal,secondVal;
cout<<"Input two hexadecimal numerals(both of them within 100 digits):\n";
cin >> firstVal >> secondVal;
//Adjust the length.
if(firstVal.size() < secondVal.size()){
//Find out the number of leading zeroes needed
int leading_zeroes = secondVal.size() - firstVal.size();
for(int i = 0; i < leading_zeroes; i++){
firstVal = '0' + firstVal;
}
}
else if(firstVal.size() > secondVal.size()){
int leading_zeroes = firstVal.size() - secondVal.size();
for(int i = 0; i < leading_zeroes; i++){
secondVal = '0' + secondVal;
}
}
// Now, perform addition.
string result;
int digit_a,digit_b,carry=0;
for(int i = firstVal.size()-1; i >= 0; i--){
if(firstVal[i] >= '0' && firstVal[i] <= '9') digit_a = firstVal[i] - '0';
else digit_a = firstVal[i] - 'A' + 10;
if(secondVal[i] >= '0' && secondVal[i] <= '9') digit_b = secondVal[i] - '0';
else digit_b = secondVal[i] - 'A' + 10;
int sum = digit_a + digit_b + carry;
if(sum > 15){
carry = 1;
sum = sum % 16;
}
else{
carry = 0;
}
// Convert sum to char.
char char_sum;
if(sum >= 0 && sum <= 9) char_sum = sum + '0';
else char_sum = sum - 10 + 'A';
//Append to result.
result = result + char_sum;
}
if(carry > 0) result = result + (char)(carry + '0');
//Result is in reverse order.
reverse(result.begin(),result.end());
cout << result << endl;
}

C++ character counter

I need to design a character counter, whenever I enter single char. it gives me the next one in succession e.g. enter A, it shows B, Z-->A for both lower and Upper letters. only using (for loop)
What went wrong?
The characters doesn't show in order I mean whenever I enter a letter it's random response giving me a random number that hasn't any function of the program the body looks acceptable but in turns of internal details something isn't going the way I wanted to be. Here's my code:
char count[256];
int size = 0;
for ( c != 0; ((c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z')) ; c++ )
{
size += count[c];
}
return size;
return 0;
using ASCI codes will be helpfull here
for e.g
char alphabet ;
cout <<"Enter alphabet"<<endl;
cin>>alphabet ;
int a = (int) alphabet;
a++;
cout<<"Next alphabet is :"<<(char)a<<endl ;
Take your input
Check if it is an alphabet
Check if it is a 'z' or 'Z', if so, make it an 'a', or 'A' (hint: use ascii codes and a little arithmetic)
Else add a character to it
Print

How to display char character as an int, not as the ASCII symbol

I need this character to display as a number but I keep getting smiley faces and hearts and other ASCII symbols. This part is where I think the problem is:
s = prefix + ch + '.';
And here's the whole code:
int main()
{
int levels = 2;
string prefix = "Recursion:";
sections(prefix, levels);
system("pause");
return 0;
}
void sections(string prefix, int levels)
{
if (levels == 0)
{
cout << prefix << endl;
}
else
{
for (char ch = 1; ch <= 9; ch++)
{
string s;
s = prefix + ch + '.';
sections(s, levels - 1);
}
}
}
You're using int values for your characters, rather than characters, so you will get whatever characters happen to have those codes in your character set. Use ' arounds a character to get the character code for a specifiec character:
for (char ch = '1'; ch <= '9'; ch++)
sections(prefix + ch + '.', levels - 1);
Note that this depends on the digit characters all being contiguous and in ascending order in your character set (implementation defined), but that is the case for every character set I can think of...
You should use std::to_string function to convert the number into string.
The problem is your for-loop
char ch = 1 //is not a 1
char ch = '1' //instead is (but i'm not sure if you can increment this)
char ch = 49 // is also a 1
hope that helps.
https://en.wikipedia.org/wiki/ASCII

C++ caesar cipher — understanding ascii keys

I am currently doing a caesar cipher program. It should encrypt for both lower and upper case.
e.g
If I typed in a, it will then shift the keys by 3 and the final output will become d.
Take a look at my codes
char c;
c = (((97-52)+3) % 26) + 52;
cout << c;
The letter 'a' has an ASCII code of 97.
So by right
1) ((97-52)+3) will give you 48
2) 48 % 26 will give you 8 since 48/26 will give you a remainder of 8.
3) 8 + 52 = 60(which will by right give you a value of '>' according to the ascii table)
but my output that I have got is J and I don't understand which am I getting the output of 'J' instead of '>'
My concepts might be wrong so I need help.
Let me link ASCII chart I use first: http://pl.wikipedia.org/wiki/ASCII
The website is polish, but table itself is in english.
I think it's plainly obvious that problem is the equatation you use:
(((letter-52)+3) % 26) + 52;
Actually first letter in ASCII is 65(hexadecimal 0x41 - follow with the chart provided).
Your idea with the modulo would be fine, if there were no chars between letter blocks in ASCII. But there are (again check up chart).
That is why you should manually check if the sign:
is a capital letter: if (letter >= 0x41 && letter <= 0x5a)
is a non-capital: if (letter >= 0x61 && letter <= 0x7a)
Usually when making Ceasar cipher, you should follow these:
Replace a capital letter with capital letter moved in the alphabet by a given number.
If the letter would be out of alphabet scope, continue iteration from the start of alphabet (X moved 5 to the right would give C).
Other chars stay the same
Now let's implement this (in code I'll use letter values of chars - to avoid mistakes):
#include <iostream>
#include <cstdlib>
using namespace std;
string Ceasar(string input, int offset)
{
string result = "";
for (int i = 0; i < input.length(); ++i)
{
// For capital letters
if (input[i] >= 'A' && input[i] <= 'Z')
{
result += (char) (input[i] - 'A' + offset) % ('Z' - 'A') + 'A';
continue;
}
// For non-capital
if (input[i] >= 'a' && input[i] <= 'z')
{
result += (char) (input[i] - 'a' + offset) % ('z' - 'a') + 'a';
continue;
}
// For others
result += input[i];
}
return result;
}
int main()
{
cout << Ceasar(string("This is EXamPLE teXt!?"), 8).c_str();
system("PAUSE");
}

How does this array conversion work ( lowercase to uppercase using a string)?

I got the program to work as expected, but can anyone explain how it works?
#include <iostream>
using namespace std;
int main(void) {
int exit;
string name;
cin >> name;
for (int i = 0; i < name.length(); i++) {
// the line below is the one I don't understand
if ('a' <= name[i] && name[i] <= 'z') name[i] = char(((int)name[i]) - 32);
}
cout << name;
cin >> exit;
return 0;
}
EDIT: Let me rephrase:
The thing I don't understand is how does the string-to-array deal work, as in:
'a'<= name[i]. What exactly does this compare and how?
EDIT2
Thanks for the quick responses guys, love you all. I figured it out.
This is the line:
if('a'<=name[i] && name[i]<='z')name[i]=char(((int)name[i])-32);
broken down:
if( 'a'<=name[i] ) {
if( name[i]<='z' ) {
// name_int is a temporary, which the above code implicitly creates,
// but doesn't give a name to:
int name_int = name[i];
name_int = name_int - 32;
name[i] = char(name_int);
}
}
and note that 32 happens to equal 'a'-'A' in the character encoding you are using.
(Technically name_int should be an int&& or somesuch, but no need to be that confusing.)
I assume from the edit in your comment that you are wondering how the [] can apply to a string object. The operator [] is overloaded for string to return a reference to the character at the specified position offset of the represented string. There need not be any direct conversion of the string into an array. The code that implements the overload could well be walking a linked list. It depends on how string was implemented.
It assumes ASCII character format where to convert from lowercase to uppercase you subtract 32 from the original ASCII value. This is because the ASCII values for uppercase are smaller than those for lower case and it's a constant difference between A and a, B and b and so on.
For reference: http://www.asciitable.com/
'a' <= name[i] && name[i] <= 'z'
This line is comparing the corresponding ASCII values of these two characters. 'a' in ASCII is 97 and 'z' is 122. If name[i] is one of the characters from 'a' to 'z' the expression returns true. This is commonly used to check if a variable is alphabetic.
if ('a' <= name[i] && name[i] <= 'z')
char objects are numeric values similar to ints. So 'a' <= name[i] is simply testing if the numeric value of 'a' is less than or equal to the character you're examining. Combined with name[i] <= 'z' and you're testing if the numeric value of name[i] is between the values of 'a' and 'z'. Now, it just so happens that the most common scheme for assigning numeric values to chars, named "The American Standard Code for Information Interchange" (ASCII), has the alphabet arranged in order; 'a' + 1 = 'b', 'b' + 1 = 'c', and so on. So figuring out if the character is between 'a' and 'z' tells you if it's a lower case letter.
name[i] = char(((int)name[i]) - 32);
Once you know that chars are just numeric values you might infer from the basic properties of arithmetic which we all learned in grade school that 'a' + ('A' - 'a') results in the value 'A'. Further, ASCII has the upper case alphabet arranged similarly to the lower case alphabet so that 'A' + 1 = 'B', etc. So taking anycharin the lower case alphabet and adding'A' - 'a'will result in the upper case version of that letter. In ASCII'A' - 'a'` happens to have the value -32. So take the numeric value for a lower case letter, subtract 32, and you have the value for the upper case letter.
For comparison here's a version of the code that doesn't depend on ASCII:
auto l = std::locale();
if (std::islower(name[i], l))
name[i] = std::tolower(name[i], l);