Weird output when printing in C - c

Question

Just started C after first year of java and am already confused. I try to print an array into a multiplication table. It works otherwise but I get zeroes after the first round of printing the array. I have allocated data in the whole array and it loops the right amount after checking. Still after the first print line I get 0 0 0 0 0 0 0 after the correct output.
#include<stdio.h>
int main(void)
{
int kertotaulu[15] = {1,2,3,4,5,6,7,8,9,10,11,12,13,14,15};
int kertoja;
int indeksi;
for(kertoja = 0; kertoja <=15; kertoja++) {
if(kertoja == 0) {
printf("x");
printf(" ");
for(indeksi = 0; indeksi< (sizeof(kertotaulu) / sizeof(kertotaulu[0])); indeksi++) {
printf("%d", kertotaulu[indeksi]);
printf(" ");
}
}
for(indeksi = 0; indeksi< (sizeof(kertotaulu) / sizeof(kertotaulu[0])); indeksi++) {
printf("%d", kertotaulu[indeksi]*kertoja);
printf(" ");
}
printf("\n");
}
return 0;
}
and the output is:
x 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
2 4 6 8 10 12 14 16 18 20 22 24 26 28 30
3 6 9 12 15 18 21 24 27 30 33 36 39 42 45
4 8 12 16 20 24 28 32 36 40 44 48 52 56 60
5 10 15 20 25 30 35 40 45 50 55 60 65 70 75
6 12 18 24 30 36 42 48 54 60 66 72 78 84 90
7 14 21 28 35 42 49 56 63 70 77 84 91 98 105
8 16 24 32 40 48 56 64 72 80 88 96 104 112 120
9 18 27 36 45 54 63 72 81 90 99 108 117 126 135
10 20 30 40 50 60 70 80 90 100 110 120 130 140 150
11 22 33 44 55 66 77 88 99 110 121 132 143 154 165
12 24 36 48 60 72 84 96 108 120 132 144 156 168 180
13 26 39 52 65 78 91 104 117 130 143 156 169 182 195
14 28 42 56 70 84 98 112 126 140 154 168 182 196 210
15 30 45 60 75 90 105 120 135 150 165 180 195 210 225

Answer 1

kertoja is zero the first time through the loop so your second indeksi loop multiplies each element by zero giving you all of the extra 0's. You could add the second indeksi loop into an else case to avoid this, I'm not sure exactly what output you're looking for however so...

Answer 2

The issue could be fixed by ommitting the second loop for the index 0 as follows.
int main(void)
{
int kertotaulu[15] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 };
int kertoja;
int indeksi;
for (kertoja = 0; kertoja <= 15; kertoja++)
{
if (kertoja == 0)
{
printf("x");
printf(" ");
for (indeksi = 0; indeksi < (sizeof(kertotaulu)
/ sizeof(kertotaulu[0])); indeksi++)
{
printf("%d", kertotaulu[indeksi]);
printf(" ");
}
}
else // <-- change
{
for (indeksi = 0; indeksi < (sizeof(kertotaulu)
/ sizeof(kertotaulu[0])); indeksi++)
{
printf("%d", kertotaulu[indeksi] * kertoja);
printf(" ");
}
}
printf("\n");
}
return 0;
}

Answer 3

For the case when kertoja is zero it does it's own loop, but it also continues on to the second loop. A simple new line and continue should fix it.
#include<stdio.h>
int main(void)
{
int kertotaulu[15] = { 1,2,3,4,5,6,7,8,9,10,11,12,13,14,15 };
int kertoja;
int indeksi;
for (kertoja = 0; kertoja <= 15; kertoja++) {
if (kertoja == 0) {
printf("x");
printf(" ");
for (indeksi = 0; indeksi < (sizeof(kertotaulu) / sizeof(kertotaulu[0])); indeksi++) {
printf("%d", kertotaulu[indeksi]);
printf(" ");
}
printf("\n"); // New Line
continue; // Continue, goes to the top of loop again
}
for (indeksi = 0; indeksi < (sizeof(kertotaulu) / sizeof(kertotaulu[0])); indeksi++) {
printf("%d", kertotaulu[indeksi] * kertoja);
printf(" ");
}
printf("\n");
}
return 0;
}