Character Arrays in C

[raddmadd]

I understand simple character arrays; however I do not understand this code example in the K & R book:

#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 */
main()
{
    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);
    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;
}
 

As the comment before main says, the program outputs the longest string. However, a few things I don't understand.

When I declare an array, I cannot leave the array subscript empty (int blah[]) I have to specify the subscript. However in this program, the parameters for getline and copy have arrays with an empty subscript. I don't understand this and I don't understand using the array line and longest. They are being used as arguments without specifying which subscript is being used.

I may not be clear on what I do not understand, but I would like someone to explain how line and longest are being passed to the functions.

Thank you in advance.

[Natasha26]

I understand simple character arrays; however I do not understand this code example in the K & R book:

#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 */
main()
{
    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);
    return 0;
}
 

When I declare an array, I cannot leave the array subscript empty (int blah[]) I have to specify the subscript. However in this program, the parameters for getline and copy have arrays with an empty subscript. I don't understand this and I don't understand using the array line and longest. They are being used as arguments without specifying which subscript is being used.

I may not be clear on what I do not understand, but I would like someone to explain how line and longest are being passed to the functions.

Thank you in advance.

When you declare a static array, you can do either of the following:

 int arr1[3] = {1,2,3}; // or int arr1[3]; arr1[0]=1; arr1[1]=2; arr1[2]=3;
int arr2[] = {1,2,3}; //compiler creates array of 3 and initialises them with the given values
char arr3[] = "hello world!"; //compiler creates char array of length 12+1. the last character being the '\0' to indicate end of char array (this is a special case), and initialises the array with the given characters
 

When you pass an array to a function (in the 1-dimensional case), the following declarations are equivalent:

void f(char arr[], int size);
void f(char* arr, int size);

Since the function cannot know the size of the array (actually i don't think the function even knows if it's an array), you have to pass the array size as second argument, and write your code to deal with both arguments.

[whodgson]

Another variation is demonstrated with this example.
Assume you have an int array with say 20 test scores and you want to cycle through them and assign each an A or B or C etc.grade if each is > 90 or >80 or >70 etc.and accumulate the number of A`s,B`s etc.

int score [20] = (88,47,67, etc.};      //the data array
enum {A,B,C,D,F};                         //assign an integer to each grade 1-5
int freq [5] = {0};                            //declare a freq array (to hold grades A - F)
if(score[i] >=90)++freq[A];             //will accumulate no of A`s in score[]
if(score[i]>=80)++freq[B};              // will accumulate no of B`s in score[] etc.
cout<<"No of A`s"<<freq[A];           
 

I found this in a book i`m using to learn about C++ namely: Fundamentals of Computing with C++ by John R Hubbard.