Sum=0, when to use? C programming

Question

Hello everybody! I'm very new to C and I have some difficulties about when to declare sum=0 and when not to.

i.e, I want to make a multiplication table, I got it to work one way, without using sum. But when I use sum my output is very wrong and by the looks of it, it has something to do with sum.

//Code without sum

#include <stdio.h>

int main ()
{
int i, n;
printf("Input the number : ");
scanf("%d", &n);
for(i=1;i<=10;i++)
{
printf("%d X %d = %d\n", n, i, (i*n));

}
}

//Code with sum

#include <stdio.h>

int main ()
{
int i, n, sum=0;
printf("Input the number : ");
scanf("%d", &n);
for(i=1;i<=10;i++)
{
printf("%d X %d = %d\n", n, i, sum);
sum = n * i;

}
}

What did I do wrong in the last code?

output:
Input the number : 15
15 X 1 = 0
15 X 2 = 15
15 X 3 = 30
15 X 4 = 45
15 X 5 = 60
15 X 6 = 75
15 X 7 = 90
15 X 8 = 105
15 X 9 = 120
15 X 10 = 135

expected output:
Input the number : 15
15 X 1 = 15
15 X 2 = 30
15 X 3 = 45
15 X 4 = 60
15 X 5 = 75
15 X 6 = 90
15 X 7 = 105
15 X 8 = 120
15 X 9 = 135
15 X 10 = 150

What should I look for in a given task to know wether or not to include sum in my program?

Answer 1

Try to execute first sum = n* i and after the printf...
Anyway, i dont see any addition in this code.. Effectivly its like the other code but using sum var like temporary variable for contain the multiplication 🤔

Answer 2

#include <stdio.h>

int main ()
{
int i, n;
printf("Input the number : ");
scanf("%d", &n);
for(i=1;i<=10;i++)
{
printf("%d X %d = %d\n", n, i, (n*i));

}
}

Maybe this code is helpful for you try this.