The C Programming Language, Ch.1 Exercise 1.10 (Getchar and Putchar)

I've been working on this for 2 hours and I am stuck... I found the answer online, but that isn't going to help me learn the concept that I'm obviously missing.

Prompt: Write a program to copy its input to its output, replacing each tab by \t , each backspace by \b , and each backslash by \\ . This makes tabs and backspaces visible in an unambiguous way.

Here's what I came up with, it doesn't replace a tab or \ with the indicated putchar, it just adds it in front of it.(I didn't do backspace because I can't really input a backspace...):

This is how I read the code. What am I missing?:

"There is some integer c. c is equal to the input. When the input is not equal to end of file proceed. If input is tab then the output \t. If input is \ then output \\. Output the input to console."

int c;

while((c=getchar())!=EOF)
{
    if(c=='\t')
        {
            putchar('\\');
            putchar('t');
        }

    if(c=='\\')
        {
            putchar('\\');
            putchar('\\');
        }
    putchar(c);
}

Solution

Your main problem is that you are outputting the character regardless of the fact that you may have already output its translation. Those if statements will do what you expect but, in their present form, they simply drop through to the next statement.

Hence you'd be looking for something more like this:

while ((c = getchar()) != EOF) {
    // Detect/translate special characters.

    if (c == '\t') {
        putchar ('\\');
        putchar ('t');
        continue;              // Go get next character.
    }

    if (c == '\b') {
        putchar ('\\');
        putchar ('b');
        continue;              // Go get next character.
    }

    if (c == '\\') {
        putchar ('\\');
        putchar ('\\');
        continue;              // Go get next character.
    }

    // Non-special, just echo it.

    putchar (c);
}

Another possibility, shorter and more succinct would be:

while ((c = getchar()) != EOF) {
    // Detect/translate special characters, otherwise output as is.

    switch (c) {
        case '\t': putchar ('\\'); putchar ('t');  break;
        case '\b': putchar ('\\'); putchar ('b');  break;
        case '\\': putchar ('\\'); putchar ('\\'); break;
        default:   putchar (c);
    }
}