CODEWITHSUNDEEP
cstructure
Andrei Popescu
Andrei Popescu

Reputation: 17

Deleting structure in C programming

#include <stdio.h>
#include <conio.h>
#include <string.h>

typedef struct {
    char serie_calculator[45];
    char tip_procesor[78];
    char memorie[55];
    char hdd[60];
    char monitor[65];
}Calculator;

void deleting(Calculator *ct, int *dim, char serie[45])
{
    int k = 0, i, j;
    for (i = 0;i<(*dim);i++)
        if (strcmp((ct + i)->serie_calculator, serie) == 0)
        {
            k++;
            for (j = i;j < (*dim - k);j++)

                *(ct + j) = ct[j + 1]; // <== This line here

        }
    *dim = *dim - k;
}

In the deleting function, I don't understand what the line: *(ct + j) = ct[j + 1]; does. Can somebody help? I hope that you understand the function, because this is just a sequence from the whole program.

Upvotes: 1

Views: 7161

Answers (1)

Vlad from Moscow
Vlad from Moscow

Reputation: 310980

In this function

void deleting(Calculator *ct, int *dim, char serie[45])

it seems that the first parameter is declared like a pointer to the first element of the array passed to the function as an argument.

Thus

ct[0]

will denote the first element of the array

ct[1]

will denote the second element of the array and so on.

This record

ct[i]

where i is some index is equivalent to

*( ct + i )

So this statement

*(ct + j) = ct[j + 1];

can be written also like

ct[j] = ct[j + 1];

As for the function itself then it is entirely wrong.

In this loop

        for (j = i;j < (*dim - k);j++)

            *(ct + j) = ct[j + 1]; // <== This line here

that as it was said can be written also like

        for (j = i;j < (*dim - k);j++)

            ct[j] = ct[j + 1]; // <== This line here

there is an attempt to write beyond the array when j is equal to *dim - 1 because expression j + 1 in this case will be equal to *dim though the valid range of indices is [0, *dim - 1]

Also the condition in the outer loop also should look at least like

for (i = 0; i < (*dim) - k; i++)
            ^^^^^^^^^^^^^^

and the index i shall not be increased when an element of the array was deleted. Otherwise the next element after the deleted element will be skipped.

A correct implementation of the function that I named like remove_all can look the following way as it is shown in the demonstrative program below. I simplified the structure declaration because other data members of the structure are irrelevant for the function implementation.

#include <stdio.h>
#include <string.h>

typedef struct 
{
    char serie_calculator[45];
    // ...    
} Calculator;

size_t remove_all( Calculator c[], size_t n, const char *s )
{
    size_t i = 0;

    for ( size_t j = 0; j < n; j++ )
    {
        if ( !( strcmp( c[j].serie_calculator, s ) == 0 ) )
        {
            if ( i != j ) c[i] = c[j];
            ++i;
        }
    }

    return i;
}

int main(void) 
{
    Calculator c[] = { { "A" }, { "B" }, { "C" }, { "A" }, { "D" }, { "E" }, { "A" } };
    const size_t N = sizeof( c ) / sizeof( *c );

    for ( size_t i = 0; i < N; i++ ) printf( "%s ", c[i].serie_calculator );
    printf( "\n" );

    size_t n = remove_all( c, N, "A" );

    for ( size_t i = 0; i < n; i++ ) printf( "%s ", c[i].serie_calculator );
    printf( "\n" );

    return 0;
}

The program output is

A B C A D E A 
B C D E

Upvotes: 1

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