CODEWITHSUNDEEP
ccodeblocks
kpark
kpark

Reputation: 394

Creating Pascal's Triangle (Unstable Code)

There are two questions concerning the code posted below:

    1) When I run this code on CodeBlocks, the code sometimes successfully runs (returning 0) but usually results in an error after it shows all the results (returning -1073741819). Why is this the case?

    2) The values are all correct except for the last element of the array where the value should be 1 (pTriangle[20] = 1). However, I am getting some garbage number at the end, what am I doing wrong?

I have realized I could arrive at the same result with binomial coefficients but I still have no idea why I am getting the error and it'd be best if my mistake can be found.

Update1:
pTriangle[i] = temp[i % 2 ? 0 : 1] + pTriangle[i]; seems to be the problem. When I have commented this code, the program did not crash. I am trying to find out why it is crashing and trying to find a solution around it :)

#include <stdio.h>
#include <stdlib.h>

#define LEVEL 20

int main()
{
    int *pTriangle = (int*)malloc(sizeof(int)*(LEVEL+1));
    int i;

    for (i = 0; i < LEVEL; i++)
        pTriangle[i] = 0;

    createPascalTriangle(pTriangle, LEVEL);

    for(i = 0; i < LEVEL+1; i++)
        printf("pTriangle[%d]: %d\n", i, pTriangle[i]);

    free(pTriangle);

    return 0;
}

int createPascalTriangle(int *pTriangle, int level){
    if (level <= 0)
        return 0;
    pTriangle[0] = 1;
    pTriangle[1] = 1;
    int i;
    for ( i = 2; i <= level; i++)
        increasePascalTriangleOneLevel(pTriangle);

    return 1;
}

int increasePascalTriangleOneLevel(int *pTriangle){
    int i = 1;
    int temp[2] = {0};

    temp[0] = pTriangle[0];
    while (pTriangle[i] != 0){
        temp[i % 2] = pTriangle[i];
        pTriangle[i] = temp[i % 2 ? 0 : 1] + pTriangle[i];
        i++;
    }
    pTriangle[i] = 1;

    return 1;
}

Upvotes: 6

Views: 232

Answers (1)

szedjani
szedjani

Reputation: 582

The last element of the array hasn't been initialized.

Write:

for (i = 0; i < LEVEL + 1; i++)
    pTriangle[i] = 0;

instead of:

for (i = 0; i < LEVEL; i++)
        pTriangle[i] = 0;

Upvotes: 1

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