array problem

This is a discussion on array problem within the C Programming forums, part of the General Programming Boards category; there code i dont understand 1 line in it i dont understand Code: #include <stdio.h> #define MAXLINE 1000 /* maximum ...

  1. #1
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    array problem

    there code i dont understand 1 line in it i dont understand
    Code:
    #include <stdio.h>
    #define MAXLINE 1000 /* maximum input line length */
    int getline(char line[], int maxline);
    void copy(char to[], char from[]);
    /* print the longest input line */
    int main(void)
    {
        int len; /* current line length */
        int max; /* maximum length seen so far */
        char line[MAXLINE]; /* current input line */
        char longest[MAXLINE]; /* longest line saved here */
        max = 0;
        while ((len = getline(line, MAXLINE)) > 0)
             if (len > max) {
                 max = len;
                 copy(longest, line);}
             if (max > 0) /* there was a line */
                 printf("%s", longest);
        getchar();
        return 0;
    }
    /* getline: read a line into s, return length */
    int getline(char s[],int lim)
    {
        int c, i;
        for (i=0; i < lim-1 && (c=getchar())!=EOF && c!='\n'; ++i)
                s[i] = c;
        if ( c == '\n' ){
            s[i] = c;
            ++i;}
        s[i] = '\0';
        return i;
    }
    /* copy: copy 'from' into 'to'; assume to is big enough */
    void copy(char to[], char from[])
    {
         int i;
         i = 0;
         while( (to[i] = from[i]) != '\0')
             ++i;
    }
    is bigger than zero means when he reached EOF but EOF is -1 right shouldnt that be -1 not 0 ?also the int c in 2nd loop why its using s[i]=c and he didnt in the for loop set it anything to the array s ?
    Last edited by elwad; 04-22-2009 at 07:40 PM.

  2. #2
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    Greater than zero is used to determine if the line has valid data on it, or is just a blank line.

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    Even though these functions are from K&R, remove this:
    Code:
    != EOF && c
    Or, simply replace the && operator to ||. Beginners should not be using EOF in a console.

  4. #4
    DESTINY BEN10's Avatar
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    Quote Originally Posted by elwad View Post
    there code i dont understand 1 line in it i dont understand
    Code:
    #include <stdio.h>
    #define MAXLINE 1000 /* maximum input line length */
    int getline(char line[], int maxline);
    void copy(char to[], char from[]);
    /* print the longest input line */
    int main(void)
    {
        int len; /* current line length */
        int max; /* maximum length seen so far */
        char line[MAXLINE]; /* current input line */
        char longest[MAXLINE]; /* longest line saved here */
        max = 0;
        while ((len = getline(line, MAXLINE)) > 0)
             if (len > max) {
                 max = len;
                 copy(longest, line);}
             if (max > 0) /* there was a line */
                 printf("%s", longest);
        getchar();
        return 0;
    }
    /* getline: read a line into s, return length */
    int getline(char s[],int lim)
    {
        int c, i;
        for (i=0; i < lim-1 && (c=getchar())!=EOF && c!='\n'; ++i)
                s[i] = c;
        if ( c == '\n' ){
            s[i] = c;
            ++i;}
        s[i] = '\0';
        return i;
    }
    /* copy: copy 'from' into 'to'; assume to is big enough */
    void copy(char to[], char from[])
    {
         int i;
         i = 0;
         while( (to[i] = from[i]) != '\0')
             ++i;
    }
    is bigger than zero means when he reached EOF but EOF is -1 right shouldnt that be -1 not 0 ?also the int c in 2nd loop why its using s[i]=c and he didnt in the for loop set it anything to the array s ?
    what's actually is ur problem?max is the length of the the line which will always be either greater than or equal to 0(in the case the line doesn't have any character).

  5. #5
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    Quote Originally Posted by abraham2119 View Post
    Even though these functions are from K&R, remove this:
    Code:
    != EOF && c
    Or, simply replace the && operator to ||. Beginners should not be using EOF in a console.
    you absolutely do not know what you are talking about...
    The first 90% of a project takes 90% of the time,
    the last 10% takes the other 90% of the time.

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    I use tests for EOF in lots of my console functions and programs.

    You will definitely want to use EOF when you're working with text files.

    You might also remember that while K&R are merely mortals and make mistakes, they are also blatantly brilliant with their work in the C language.

    I would hesitate so many times before I said someone should change something substantive, in their famous book.

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    srry electricity was out my problem that i dont understand that getline function i understand some stuff but genrally i dont get its idea and K&R is a really great book i have just started c programming and it taught me alot of stuff.

  8. #8
    DESTINY BEN10's Avatar
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    Quote Originally Posted by elwad View Post
    srry electricity was out my problem that i dont understand that getline function i understand some stuff but genrally i dont get its idea and K&R is a really great book i have just started c programming and it taught me alot of stuff.
    the getline() function takes a line with as much as 999 characters in it and the condition is that as oon as u press EOF the line will be finished and also if '\n' is pressed the line will be changed and the last character of the lin ewill be '\n'.

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    Quote Originally Posted by BEN10 View Post
    the getline() function takes a line with as much as 999 characters in it and the condition is that as oon as u press EOF the line will be finished and also if '\n' is pressed the line will be changed and the last character of the lin ewill be '\n'.
    so in getline function s[i] = c it cr8tes the string but this check
    Code:
     if 
    (
    c == '\n') {s[i] = c;
    ++i;
    } why did he do this coz a string doesnt contain \n ?also in main
    Code:
    while ((len = getline(line, MAXLINE)) > 0)
    i thought EOF is -1 not bigger than zero ?

  10. #10
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    len refers to the length of the string, not whether the file pointer has reached the EOF.

    He wants to include the newline char, and (I believe), count it as another line of text. (++i).

  11. #11
    DESTINY BEN10's Avatar
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    Quote Originally Posted by elwad View Post
    so in getline function s[i] = c it cr8tes the string but this check
    Code:
     if 
    (
    c == '\n') {s[i] = c;
    ++i;
    } why did he do this coz a string doesnt contain \n ?also in main
    Code:
    while ((len = getline(line, MAXLINE)) > 0)
    i thought EOF is -1 not bigger than zero ?
    if u press "ENTER" the line will be changed so the last character pressed is '\n' so the loop breaks and the last character pressed is '\n' which is give by if(c=='\n').
    also len is the length of the the characters inputted by the user which will always be >=0.if the first character inputted is itself EOF then also len=0 not -1 coz -1 is the value of EOF, it doesn't give u the length of the line.

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    so when u make cntrl_z in console it will set len to -1 whish will exit loop ? or set it to 0 ?

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    also one more question why did we increment i after if(c=='\n') isnt this a new string it should add 0 to it before increment ?

  14. #14
    DESTINY BEN10's Avatar
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    when u make cntrl+z 'len' will be set to 0 coz i already told u len is the length of the line i.e how many characters does the line have. len=-1 is nothing(imagine can the length of any line be negative).
    If u press '\n' 'i' will get incremented coz '\n' is also of one character length, so the ++i is done.
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    Quote Originally Posted by elwad
    is bigger than zero means when he reached EOF but EOF is -1 right shouldnt that be -1 not 0 ?
    function is return i
    it isn't return EOF
    when (c=getchar()) ==EOF || c == '\n' it is not enter the loop and go to s[i] = '\0'; if it wasn't read any character (got an EOF from getchar), or it was '\n', i wasn't encreased and equal to zero, s[0] = '\0'; return 0;

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