C编程 - 浮点异常

Question

matthewmpp@annrogers:~/Programming/C.progs/Personal$ cat prime4.c
/*
 * File:   main.c
 * Author: matthewmpp
 *
 * Created on November 7, 2010, 2:16 PM
 */

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

/*
prime numbers.
version4
should tell whether a number is prime or not prime.
by using other prime numbers.
 */

int input_func ()
{
    char line[100];
    int n_input;

    while (1) {
        printf("Please enter a whole number.\n");
        fgets(line, sizeof (line), stdin);
        sscanf(line, "%d", &n_input);

        if (n_input >= 0)
            break;

        return (n_input);
    }
}

int ifstatements_func (n_ifstate)
int n_ifstate;
{
    if (n_ifstate == 0) {
        printf("The number, %d, is not prime and has no factors.\n", n_ifstate);
        exit(1);
    }

    if (n_ifstate == 1) {
        printf("The number, %d, is not prime.\n", n_ifstate);
        printf("The factors of %d, is %d.\n", n_ifstate, n_ifstate);
        exit(1);
    }

    if (n_ifstate == 2) {
        printf("The number, %d, is a prime.\n", n_ifstate);
        printf("The factors of %d, are 1 and %d.\n", n_ifstate, n_ifstate);
        exit(1);
    }
    if (n_ifstate == 3) {
        printf("The number, %d, is a prime.\n", n_ifstate);
        printf("The factors of %d, are 1 and %d.\n", n_ifstate, n_ifstate);
        exit(1);
    }
    return (n_ifstate);
}

int square_root_func (n_prmfnc)
int n_prmfnc;
{
    int i;  //counter

    float sq_root_f;
    int sq_root_i;

    int primes[100];
    int length_primes;

    primes[0] = 2; /*first prime is 2.*/
    primes[1] = 3; /*second prime is 3.*/
    length_primes = sizeof (primes);

    //printf ("before.sq_root.value of n_prmfnc=%d\n", n_prmfnc);
    sq_root_f = sqrt(n_prmfnc);
    sq_root_i = sq_root_f;
    //printf ("prmfnc.after.sq_root\n");
    //printf ("value of sq_root=%.3f\n", sq_root_f);
    //printf ("value of sq_root=%d\n", sq_root_i);

    return (sq_root_i);
}

int prime_func (sq_root_pf, n_pf)
int sq_root_pf, n_pf;
{
    int prime_counter;
    int prime_temp;
    int prime_flag=0;

    int primes_pf[100];
    int i;                  //counter

    primes_pf[0]=2;
    primes_pf[1]=3;
    primes_pf[2]=5;

    printf ("before.for.in.pf");
    for (i = 0; i <= 100; ++i) {
        printf ("after.for.in.pf");
        if (primes_pf[i] <= sq_root_pf) {
            printf ("before.modulus.in.pf");
            prime_temp = n_pf % primes_pf[i];
            printf ("after.modulus.in.pf");
            if (prime_temp == 0) {
                ++prime_counter;
                if (prime_counter == 0)
                    prime_flag = 1; /*yes, number is prime.*/
            }
        }
    }
    return (prime_flag);
}

int main() {
    int n_main1;    //number from input
    int n_main2;    //number after if statements
    int sq_root_main;    //square root of number from function
    int prime_flag_main;   //value of 1 if it is a prime

    n_main1 = input_func ();
    printf("main.after.input.function=%d.\n", n_main1);

    n_main2 = ifstatements_func (n_main1);
    printf ("main.after.ifstatments.function=%d\n", n_main2);

    sq_root_main = square_root_func (n_main2);
    printf ("main.after.square_root_func_func=%d\n", sq_root_main);

    prime_flag_main = prime_func (sq_root_main, n_main2);
    printf ("main.after.prime_func=%d\n", prime_flag_main);

    return (EXIT_SUCCESS);
}


OUTPUT:
matthewmpp@annrogers:~/Programming/C.progs/Personal$ cc -c prime4.c
matthewmpp@annrogers:~/Programming/C.progs/Personal$ cc -o prime4 prime4.c -lm
matthewmpp@annrogers:~/Programming/C.progs/Personal$ ./prime4
Please enter a whole number.
44
main.after.input.function=44.
main.after.ifstatments.function=44
main.after.square_root_func_func=6
Floating point exception
matthewmpp@annrogers:~/Programming/C.progs/Personal$ 

声明:错误发生在prime_func中.我相信原因是模数(%符号).

问题:为什么我得到浮点异常以及如何修复它？

Answer 1

发生的是零除.您只初始化前三个条目primes_pf,但迭代所有条目(实际上,您的循环运行甚至超过最后一个条目;使用i < 100而不是i <= 100修复此问题).对于除前三个条目之外的所有条目,您除以一些单位化数量,其中一个条目显然恰好为零.不要使用单位化值.

Answer 2

"浮点异常"用词不当.它只发生在整数除以零和一些其他与除法相关的操作上.