sort.c(13) : error C2371: 'shellSort' : redefinition; different basic types

[AlexC]

program in C, shell sort.

i've got this error : sort.c(13) : error C2371: 'shellSort' : redefinition; different basic types

#include <stdio.h>
 
int a[6] = {5, 9 , 2, 8, 7, 1};
int main(){
    int m;
    m = 0;
    shellSort(a, 6);
    for(m = 0; m<20; m++)
        printf("\n%d", a[m]);
 
    return 0;
}
void shellSort( int a[],int N){
    int i, j, inc;
    int tmp;
    for(inc = N/2; inc>0; inc /= 2)
        for(i = inc; i < N; i ++)
        {
            tmp = a[i];
            for(j = i; j>= inc; j -= inc)
                if(tmp <a[j-inc])
                    a[j] = a[j - inc];
                else 
                    break;
            a[j] = tmp;
        }
 
}
 

[Banfa]

Is that the only message you get nothing on line 7?

You called shellSort at line 7, it wasn't prototyped so the C compiler automatically assigned as a prototype returning int it declared it as

int shellSort();

Then at line 15 you define it as

void shellSort( int a[],int N)

And you get an error because you have defined it as returning void but the compiler declared it as returning int.

Predeclare you function at line 2 to avoid this.

[AlexC]

Thanks, I need to study so much. I didn't know that.
this is fixed up code

#include <stdio.h>
 
int a[6] = {5, 9 , 2, 8, 7, 1};
int main(){
    int m;
    m = 0;
    printf("Unsorted list:");
    for(m = 0; m<6; m++)
        printf("\n%d", a[m]);
    shellSort(a, 6);
    printf("\nShell Sorted: ");
    for(m = 0; m<6; m++)
        printf("\n%d", a[m]);
 
    return 0;
}
int shellSort( int a[],int N){
    int i, j, inc;
    int tmp;
    for(inc = N/2; inc>0; inc /= 2)
        for(i = inc; i < N; i ++)
        {
            tmp = a[i];
            for(j = i; j>= inc; j -= inc)
                if(tmp <a[j-inc])
                    a[j] = a[j - inc];
                else 
                    break;
            a[j] = tmp;
        }
return 0;
}