C++ programming help needed

[jjones237]

Can anybody run through the steps it takes to get the output for this problem? This is a practice example I was given. Help is appreciated.


#include <stdio.h>

#include <ctype.h>

int main() {

char c;

while ((c = getchar()) != '0') {

if (isupper(c))

putchar(('A' + 15-(c-'A')));

else if (islower(c))

putchar(('a' + 5 +(c-'a')) );

else

putchar(c);
}

return 0;
}

[jjones237]

The input is : aBcD!0

[abraxas334]

So I guess the ouput is fOhM! But you knew that already.
What does the program do?
http://www.cplusplus.com/reference/clibrary/cstdio/putchar/
the function putchar returns the character onto the screen.
It is actually working on it as the int value/ascii value.
So upper case A has the value of 65.


putchar(('a' + 5-(c-'a'))); //here c is 'a'
This becomes in mathematical terms for the first input character:
97+5-(97-97) = 102 -> this corresponds to the ascii charakter of 'f'
the the next letter is capital so it will go into this one:

putchar(('A' + 15-(c-'A'))); //where the character is B
following the same scheme:
ASCII value for A = 65 B=66
65+15-(1)= 79 -> ASCII is 'O'

I assume this explains the output. Here is a list for all the ASCII codes in case you don't have them in mind like me.
http://www.ascii-code.com/