Why program is giving unexpected output? - c

Question

I'm stuck in a problem given in a book. The problem is -
The prototypical Internet newbie is a fellow name B1FF,who has a unique way of wriring messages.Here’s a typical B1FF communique.:
H3Y DUD3, C 15 R1LLY C00L
Write a “B1FF filter” that reads a message entered by the user and translates it into B1FF-speak:
Enter message: Hey dude, C is rilly cool
In B1FF-speak : H3Y DUD3, C 15 R1LLY C00L
Your program should convert the message to upper-case letters,substitute digits for certain letters (A=4,B=8,E=3,I=1,O=0,S=5).
My Program-
#include<stdio.h>
int main()
{
char arr[50]={0},ch[50]={0};
int i=0;
printf("\nenter the sentence : ");
while(arr[i-1]!='\n')
{
scanf("%c",&arr[i]);
i++;
}
i=0;
while(arr[i]!='\n')
{
if(arr[i]=='e')
ch[i]='3';
if(arr[i]==('A'||'a') )
ch[i]='4';
if(arr[i]==('B'||'b'))
ch[i]='8';
if(arr[i]==('I'||'i'))
ch[i]='1';
if(arr[i]==('o'||'O'))
ch[i]='0';
if(arr[i]==('S'||'s'))
ch[i]='5';
else ch[i]=arr[i]-32;
i++;
}
ch[i]='\n';
i=0;
printf("\nIn B1FF-SPEAK : ");
while(ch[i]!='\n')
{
printf("%c",ch[i]);
i++;
}
printf("\n");
return 0;
}
OUTPUT OF THE PROGRAM-
I don't understand why the program is not converting the alphabets and why scanf() is not accepting space as a character ?

Answer 1

First and foremost, you cannot chain the logical OR operator like
if(arr[i]==('A'||'a') )
and get what you're expecting, because this resolves to an always TRUE condition. [('A'||'a') evaluates to TRUE]
You have to use
if ( (arr[i]=='A') || (arr[i] =='a'))
That said,
ch[i]=='8';, ch[i]==1; are basically empty statements. You're comparing and discarding the comparison result. If you want assignment, you need to use =.
the else ch[i]=arr[i]-32; only binds with the previous if statement, no the whole if chains. You can either make use of switch case or if-else if-else constructs to take care of that part.
you did not handle whitespaces separately.
To elaborate, due to the second point above, you code basically reduces to
while(arr[i]!='\n')
{
if(arr[i]==('S'||'s')) //always false
ch[i]='5';
else ch[i]=arr[i]-32; //always TRUE
i++;
}
which is just a poor attempt to convert lowercase to UPPERCASE. In case a non-alpha input is there in the string, the code will blow up.
That said, regarding the
why scanf() is not accepting space as a character?
part, scanf() perfectly accepts a space as an input with %c, it's you just convert it no NUL (null) by blindly subtracting 32 from a space which has an ASCII value of decimal 32. A NUL is non printable, and does not appear in the output.

Answer 2

Some recommendations:
Don't use lots of little calls to scanf("%c"...). Use fgets() (manpage). fgets reads in a whole line from input, stores it in your buffer (including the newline), and sticks a '\0' byte at the end of it so you know how long the string is.
use toupper() (manpage). It takes an arbitrary character as input. If the input is a lower case letter, then the output is the upper-case version of that letter. Otherwise, the output is the same as the input.
Update the array in-place. You don't need two arrays. Read the array with fgets(), loop over it with your translation logic, updating each character as you go, then write the array out with fputs().
Learn about switch statements. A switch statement will make your code more compact and easier to read. You need one case for every letter->number transform, and a default case for everything else.
c = toUpper(c);
switch (c) {
case 'A': c = '4'; break;
case 'B': c = '8'; break;
....
default: break;
}