Question

I have an array of the ‘struct student’ in c.

struct student
{
    int id;
    char *name;
    int age;       
}

int n = 100; //number of students
struct student s[n] = ...

And I have sortByField function (Bubble sort) to sort the array in order of specific field.

void sortByField(struct student *s, int n, int fieldIndex)
{
    int i, j;
    for(i=n-1; i>0; i--)
    {
        for(j=0; j<i; j++)
        {
            switch (fieldIndex)
            {
                case 1 : if(s[j].id>s[j+1].id) swapData(&s[i], &s[j+1]); break;
                case 2 : if(strcmp(s[j].name, s[j+1].name)>0) swapData(&s[i], &s[j+1]); break;
                case 3 : if(s[j].age>s[j+1].age) swapData(&s[i], &s[j+1]); break;
            }
        }
    }
}

For example, if I pass 1 to the parameter fieldIndex

sortByField(s, n, 1);

it will sort the array by id. Or, if I pass 2, it will sort by name. And so on.

Just as you saw. I used the switch-case in the loop of bubble sort to determine which field is be to compare or sort by.
But I don’t like this, I think it is redundant to must check for cases of fieldIndex again and again in the loop.

I have been trying on moving the switch-case out of the loop in order for it to be checked just once, but I am at my wit’s end.

Answer 1

void sortById(struct student *s, int n)
{
    int i, j;
    for(i=n-1; i>0; i--)
        for(j=0; j<i; j++)
            if(s[j].id>s[j+1].id)
                swapData(&s[i], &s[j+1]);

}
void sortByName(struct student *s, int n)
{
    int i, j;
    for(i=n-1; i>0; i--)
        for(j=0; j<i; j++)
            if(strcmp(s[j].name, s[j+1].name)>0)
                swapData(&s[i], &s[j+1]);

}
void sortByAge(struct student *s, int n)
{
    int i, j;
    for(i=n-1; i>0; i--)
        for(j=0; j<i; j++)
            if(s[j].age>s[j+1].age)
                swapData(&s[i], &s[j+1]);

}
void sortByField(struct student *s, int n, int fieldIndex)
{
    switch (fieldIndex)
    {
        case 1 : sortById(s, n); break;
        case 2 : sortByName(s, n); break;
        case 3 : SortByAge(s, n); break;
    }
}

But this switch isnt a big deal. And if it is you should consider more effective sort algorithm first…