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Arslong-Vitabrevis
Asked: 2022-07-18 06:17:56 +0800 CST 2022-07-18 06:17:56 +0800 CST

Why is the floating point exception (core dumped) error generated?

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I was trying to solve a project Euler problem ( number 3 ), but I get the error stating " floating point exception (core dumped) ". To tell the truth I don't know the reason for this error (I'm new to C and programming in general), this is the code:

#include <stdio.h>

int fprimos(long long int x){
    long long int i;
    int f;
    while (i < x){
        i++;
        if (x % i == 0){
            f++;
        }
    }
    if (f == 2){
        printf("%lli, es primo", x);
    }else {
        printf("%lli", x);
    }
    return 0;
}


int main (){
    long long int number = 600851475143;
    long long int c;
    long long int v;
    long long int factores[v];

    for (c=0; c < number; c++){
        if(number % c == 0){
            factores[v] = c;
            fprimos(factores[v]);
            v++;
          }
    }
}
c

1 Answers

  1. Best Answer
    long long int v;
long long int factores[v];

    Note that vit doesn't have a value assigned at declare time factores, so what size it will ultimately be will factoresbe a complete mystery.

    In order to create factoreswith a size that allows us to store velements, we first have to know what value it is going to have v. Additionally you should use dynamic memory, since your current design has two problems:

    • It's not standard compliant, so it doesn't have to compile on all systems (other than it may not work as you'd expect)
    • factoresyou're creating it on the stack. If you vstore a large value, the stack might overflow.

    Corrected it would be like this:

    int v = 0; // No creo que necesites más de 2^31 factores

// Inicialmente solo almacenará un elmento
long long int * factores = (long long int*)malloc(sizeof(long long int));

for (c=0; c < number; c++){
    if(number % c == 0){
        factores[v] = c;
        fprimos(factores[v]);
        v++;

        // Incrementamos la cantidad de memoria asignada a factores
        factores = (long long int*)realloc(factores, (v+1)*sizeof(long long int));
      }
}

free(factores);

    With this in principle it would be. Of course, you will notice that the performance can be quite poor. The problem with this solution is that dynamic memory allocation is a slow process. If time is an important factor it is important to reduce the number of calls to mallocand realloc.

    The following example reduces the number of allocations to 10%

    int v = 0; // No creo que necesites más de 2^31 factores

// Inicialmente almacenará hasta 10 elementos
long long int * factores = (long long int*)malloc(10 * sizeof(long long int));

for (c=0; c < number; c++){
    if(number % c == 0){
        factores[v] = c;
        fprimos(factores[v]);
        v++;

        // Incrementamos, únicamente cuando hayamos llenado el array
        if (v % 10 == 0)
            factores = (long long int*)realloc(factores, (v+10)*sizeof(long long int));
      }
}

free(factores);
    • 3