Pascal's Triangle program not working

Question

I'm very new to C, although I've done a decent amount of Java before. I'm making a basic Pascal's Triangle program and I've been looking at it for an hour trying to get it working. All the logic seems correct to me but I'll probably die before I realize what's wrong. Here's the program:

#include <stdio.h>
#include <stdlib.h>
double fact(int num);

int main()
{
    int row_index = 0;
    printf("Enter the row index : ");
    scanf("%d",&row_index);
    printf("\n");
    int i;
    double output1 = 0;
    double output2 = 0;
    double output3 = 0;
    double output4 = 0;
    double output5 = 0;
    int output6 = 0;
    for(i = 0; i <= (row_index + 1); i++)
    {
        output1 = fact(row_index);
        output2 = fact(i);
        output3 = row_index - i;
        output4 = fact(output3);
        output5 = output1 / (output2 * output4);
        output6 = (int)(output5);
        printf("%i ",output6);
    }
    return 0;
}

double fact(int num)
{
    double result;
    int i;
    for(i = 1; i <= num; ++i)
        {
            result = result * i;
        }
    return result;
}

The compiler is giving me no errors, and each every time I input a number it gives this as output:

Enter the row index : 6

-2147483648 -2147483648 -2147483648 -2147483648 -2147483648 -2147483648 -2147483648 -2147483648

Numbers are less likely to go out of range if you can find a progressive algorithm which multiplies and divides a previous term, instead of trying to shoot the moon with a factorial function. Or, which builds an array by addition only of two previous array terms. — Weather Vane, Feb 15 '17 at 23:40

score 0 · Answer 1 · edited May 23 '17 at 12:25

0

In double fact(int num), the variable result should be explicitly initialized. Also, I would suggest you to define both the return value of the function and variable result to int type.

See (Why) is using an uninitialized variable undefined behavior?.

edited May 23 '17 at 12:25

Community

1
1

answered Feb 15 '17 at 23:30

Neo X

947
7
9

32-bit `int` will only be able to hold results up to 12!. – interjay Feb 15 '17 at 23:34
At least use `uint64_t` – Weather Vane Feb 15 '17 at 23:38

score 0 · Answer 2 · answered Feb 15 '17 at 23:43

At a glance, there seems to be several issues.

First:

double fact(int num)
{
    double result;
    int i;
    for(i = 1; i <= num; ++i)
    {
    result = result * i;
    }
    return result;
}

result is not initialized to anything. Maybe you need to initialize it to 1?

for(i = 0; i <= (row_index + 1); i++)
{
    output2 = fact(i);
    output3 = row_index - i;
    output4 = fact(output3);
    output5 = output1 / (output2 * output4);
}

the first time around, i == 0; which means output2 at best will be 0 (assuming its automatically initialized to 0). If output2 == 0, output5 might be undefined. I say might because of double-precision numbers it may actually not be exactly 0.

Pascal's Triangle program not working

2 Answers2