Question

Question: Can someone explain to me what the if( pos > 0) putchar('\n'); does and why it does that? Why does it check if the position is greater than 0, and if it is, put a newline character?

Write a program to fold long input lines into two or more shorter lines after the last non-blank character that occurs before the n-th column of input. Make sure your program does something ntelligent with very long lines, and if there are no blanks or tabs before the specified column.

Solution

/* fold, to fold long lines after a specified Column */

#include

#define MAXCOL 50
#define TABVAL 8

char line[MAXCOL];
int expandtab(int pos);
int printline(int pos);
int getblank(int pos);
int newposition(int pos);

int main(void)
{
    int pos,c;
    pos = 0;

    while((c=getchar())!=EOF)
    {
        line[pos] = c;

        if( c == '\t')
            pos = expandtab(pos);
        if( c == '\n')
        {
            printline(pos);
            pos = 0;
        }
        else if( ++pos >= MAXCOL )
        {
            pos = getblank(pos);
            printline(pos);
            pos = newposition(pos);
        }
    }
    return 0;
}

int expandtab(int pos)
{
    line[pos] = ' ';

    for(++pos; (pos < MAXCOL)&&((pos % TABVAL)!= 0); ++pos)
    line[pos] = ' ';

    if( pos >= MAXCOL)
    {
        printline(pos);
        return 0;
    }
    else
        return pos;
}

int printline(int pos)
{
    int i;
    for(i = 0; i < pos; ++i)
        putchar(line[i]);
    if( pos > 0)
        putchar('\n');
}

int getblank(int pos)
{
    if( pos > 0)
        while( line[pos] != ' ')
            --pos;
    if(pos == 0)
        return MAXCOL;
    else
        return pos + 1;
}
int newposition( int pos)
{
    int i,j;

    if(pos <= 0 || pos >= MAXCOL)
        return 0;
    else
    {
        i = 0;
        for(j=pos;j < MAXCOL; ++j,++i)
        line[i] = line[j];  
    }
    return i;
}
    

Answer 1

Please find the answer to your question:

what the if( pos > 0) putchar('\n'); does and why it does that?

In the function printline it takes input as the position till the characters arr read for 1 column. Now when it prints the character of the one line first it prints the character to the console using the first for loop:

 for(i = 0; i < pos; ++i)
        putchar(line[i]);

then in the next line it checks if that line actually contains a character or not because if it contains the characters then the value of pos must be greater then 0 and that means that this line needs to end. So it's giving input as the

putchar('\n');

which print the new line to the console. "\n" is an escape sequence to print the new line on the console in the C language and many other languages. It indicates compiler to print the new line on the console whenever there is "\n"