Printf give an undefined behavior while using Struct in C

Question

I'm new to C Programming. Im really confused why printf gives undefined behavior output. I tried to double-check every command and I don't think there is a mistake with my current knowledge. What was wrong with my code?

struct Barang
    {
        int Kode;
        int Jumlah;
        int HargaSatuan;
        float Total;
        char Nama[20];
    }Brg[10];

    int i,j,harga=0,banyak;
    float rata=0;
    printf("Berapa banyak barang? : ");
    scanf("%d",&banyak);
    for (i=0;i<banyak;i++)
    {
        printf("\nBarang Ke-%d\n",i+1);
        printf("Masukkan Kode : ");
        scanf("%d",&Brg[i].Kode);
        fflush(stdin);
        printf("Masukkan Nama Barang  : ");
        fgets(Brg[i].Nama,20,stdin);
        strtok(Brg[i].Nama, "\n" );
        printf("Masukkan Harga Satuan : ");
        scanf("%d",&Brg[i].HargaSatuan);
        printf("Ada Berapa Jumlah?    : ");
        scanf("%d",&Brg[i].Jumlah);
        harga+=Brg[i].HargaSatuan;
    }
    for (i=0;i<banyak;i++)
    {
        printf("\nBarang Ke-%d\n",i+1);
        printf("Kode         :  %d\n",Brg[i].Kode);
        printf("Nama Barang  : %s\n",Brg[i].Nama);
        printf("Harga Satuan : %d\n",Brg[i].HargaSatuan);
        printf("Jumlah       : %d\n",Brg[i].Jumlah);
    }
    j=i;
    Brg[i].Total=(float)(Brg[i].HargaSatuan*Brg[i].Jumlah);
    rata=(float)Brg[i].Total/j;
    printf("\nTotal Harga Semua Barang : %.2f\n",Brg[i].Total);
    printf("Rata-Rata Harga Barang     : %.2f\n",rata);

If I run it

Berapa banyak barang? : 2

Barang Ke-1
Masukkan Kode : 20
Masukkan Nama Barang  : Tes A
Masukkan Harga Satuan : 20
Ada Berapa Jumlah?    : 1

Barang Ke-2
Masukkan Kode : 10
Masukkan Nama Barang  : Tes B
Masukkan Harga Satuan : 30
Ada Berapa Jumlah?    : 2

Barang Ke-1
Kode         :  20
Nama Barang  : Tes A
Harga Satuan : 20
Jumlah       : 1

Barang Ke-2
Kode         :  10
Nama Barang  : Tes B
Harga Satuan : 30
Jumlah       : 2

Total Harga Semua Barang : 2093416448.00
Rata-Rata Harga Barang     : 1046708224.00

Process returned 0 (0x0)   execution time : 21.303 s
Press any key to continue.

It give me very wrong output and unexpected. The right output should be like this:

Berapa banyak barang? : 2

Barang Ke-1
Masukkan Kode : 20
Masukkan Nama Barang  : Tes A
Masukkan Harga Satuan : 20
Ada Berapa Jumlah?    : 1

Barang Ke-2
Masukkan Kode : 10
Masukkan Nama Barang  : Tes B
Masukkan Harga Satuan : 30
Ada Berapa Jumlah?    : 2

Barang Ke-1
Kode         :  20
Nama Barang  : Tes A
Harga Satuan : 20
Jumlah       : 1

Barang Ke-2
Kode         :  10
Nama Barang  : Tes B
Harga Satuan : 30
Jumlah       : 2

Total Harga Semua Barang : 70
Rata-Rata Harga Barang     : 23.3

Process returned 0 (0x0)   execution time : 21.303 s
Press any key to continue.

How do I solve this? Thank you.

Answer 1

When you do

Brg[i].Total=(float)(Brg[i].HargaSatuan*Brg[i].Jumlah);
rata=(float)Brg[i].Total/j;

you are outside the loop, which means that i will be an index out of range of your initialized data.

For your input with two entries in the array, the valid indexes will be 0 and 1. The value of i after the loop will be 2.

You need a separate total variable that you modify inside the loop.

Answer 2

You have an error in your loop:

for (i=0;i<banyak;i++)
{
    printf("\nBarang Ke-%d\n",i+1);
    printf("Kode         :  %d\n",Brg[i].Kode);
    printf("Nama Barang  : %s\n",Brg[i].Nama);
    printf("Harga Satuan : %d\n",Brg[i].HargaSatuan);
    printf("Jumlah       : %d\n",Brg[i].Jumlah);
}
j=i;
Brg[i].Total=(float)(Brg[i].HargaSatuan*Brg[i].Jumlah);
rata=(float)Brg[i].Total/j;
printf("\nTotal Harga Semua Barang : %.2f\n",Brg[i].Total);

When the loop is done, i = banyak, but values for Brg[i] are only defined for i up to banyak - 1. I think what you meant was:

float total = 0;
for (i = 0; i < banyak; i++) {
    printf("\nBarang Ke-%d\n",i+1);
    printf("Kode         : %d\n",Brg[i].Kode);
    printf("Nama Barang  : %s\n",Brg[i].Nama);
    printf("Harga Satuan : %d\n",Brg[i].HargaSatuan);
    printf("Jumlah       : %d\n",Brg[i].Jumlah);
    Brg[i].Total = (float)(Brg[i].HargaSatuan * Brg[i].Jumlah);
    total += Brg[i].total;
}
rata = total / banyak;
printf("\nTotal Harga Semua Barang : %.2f\n",total);