How does array notation make a difference in this program?

Question

So I have a simple C program that calculates the sum of elements in an array. The problem, as it appears to me, is the notation int[] arr. Apparently, the correct notation expected is int arr[]. On running my program with the first notation, I got some eight errors. When none of the errors made sense to me, I just used the second array notation, and it worked.

Here's the code-

#include <stdio.h>

int sumOfArray(int[], int);

int main()
{
    int[] A={1,2,3,4,5};
    int sum=0;
    int size=sizeof(A)/sizeof(A[0]);
    sum=sumOfArray(A,size);
    printf("\n The sum of the array is: %d\n", sum);
    return 0;
}

int sumOfArray(int[] arr, int n)
{
    int sum=0,x;
    for (x=0; x<n; x++) {
        sum+=arr[x];
    }
    return sum;
}

If it helps, here are the errors generated:

p6.c:15:8: error: expected identifier or '('
    int[] A={1,2,3,4,5};
       ^
p6.c:17:21: error: use of undeclared identifier 'A'
    int size=sizeof(A)/sizeof(A[0]);
                    ^
p6.c:17:31: error: use of undeclared identifier 'A'
    int size=sizeof(A)/sizeof(A[0]);
                              ^
p6.c:18:20: error: use of undeclared identifier 'A'
    sum=sumOfArray(A,size);
                   ^
p6.c:23:22: error: expected ')'
int sumOfArray(int[] arr, int n)
                     ^
p6.c:23:15: note: to match this '('
int sumOfArray(int[] arr, int n)
              ^
p6.c:23:5: error: conflicting types for 'sumOfArray'
int sumOfArray(int[] arr, int n)
    ^
p6.c:11:5: note: previous declaration is here
int sumOfArray(int[], int);
    ^
p6.c:23:19: error: parameter name omitted
int sumOfArray(int[] arr, int n)
                  ^
p6.c:26:17: error: use of undeclared identifier 'n'
    for (x=0; x<n; x++) {
                ^
p6.c:27:14: error: use of undeclared identifier 'arr'
        sum+=arr[x];
             ^

I was under the impression that both array notations are acceptable. In fact, int[] arr is advised in many cases. But then what went wrong here? Any suggestions?

Many thanks!

Please mark the correct answer by clicking on the greyed-out tick. Would help a lot of people :) — Augmented Jacob, Feb 19 '15 at 07:57

Augmented Jacob · Accepted Answer · 2015-06-09T02:24:41.963

3

You must be confusing yourself with Java.

int arr[] is the general syntax with C and C++ as it means integer of a variable that is an array

But with Java, int[] arr is used as it means arr is of type integer array. (sort of)

edited Jun 09 '15 at 02:24

answered Feb 18 '15 at 03:17

Augmented Jacob

1,567
19
45

1

more specifically: in Java, apart from some special syntax regarding arrays (`int[] arr` is usual in Java, and `int arr[]` is only provided for familiarly with C), types always precede variable names in declarations. – user253751 Feb 18 '15 at 03:36

score 2 · Answer 2 · answered Feb 18 '15 at 03:21

The code shoul be like this

#include <stdio.h>

int sumOfArray(int[], int);

int main()
{
    int A[]={1,2,3,4,5};
    int sum=0;
    int size=sizeof(A)/sizeof(A[0]);
    sum=sumOfArray(A,size);
    printf("\n The sum of the array is: %d\n", sum);
    return 0;
}

int sumOfArray(int arr[], int n)
{
    int sum=0,x;
    for (x=0; x<n; x++) {
        sum+=arr[x];
    }
    return sum;
}

score 1 · Answer 3 · edited May 23 '17 at 12:05

int[] arr is not the correct way to declare the array in C. int arr[] is the correct way (More can be found in here)

About Errors : Errors are thrown due to incorrect declaration of array. Even defining the array parameter in method declaration.

Corrected code

#include <stdio.h>

int sumOfArray(int[], int);

int main()
{
    int A[]={1,2,3,4,5}; // int A[5]={1,2,3,4,5}  too is valid
    int sum=0;
    int size=sizeof(A)/sizeof(A[0]);
    sum=sumOfArray(A,size);
    printf("\n The sum of the array is: %d\n", sum);
    return 0;
}

int sumOfArray(int arr[], int n)
{
    int sum=0,x;
    for (x=0; x<n; x++) {
        sum+=arr[x];
    }
    return sum;
}

Added : int[] arr is valid in languages like C# and java don't confuse it with C

How does array notation make a difference in this program?

3 Answers3