c - 多项式操作

Question

我想添加两个多项式并在多项式结果上设置结果我对第三个函数有问题，请指出我确实需要帮助 PS:动态声明!看来我不太理解指针，所以如果你向我提出任何可以帮助我理解本章的建议，那将会很有帮助!

     typedef struct {
            int degree;
            float* coeff_tab;
        } Polynome;


        Polynome lire_polynome()
        {
            Polynome p;
            int i;

            printf("Degree du polynome? ");
            scanf("%d", &p.degree);
            p.coeff_tab = (float*)malloc((unsigned long)(p.degree+1)*sizeof (float));

            for(i=0; i<=p.degree; i++)
            {
                printf("coeff de degree %i: ", i);
                scanf("%f", &p.coeff_tab[i]);
            }
            //free(p.coeff_tab);

            return p;
        }


        void affiche_polynome(Polynome p)
        {
            int i;
            if(p.degree > 1){
                printf("%4.2fX^%i ", p.coeff_tab[p.degree], p.degree);
                for(i=p.degree-1; i>1; i--){
                    printf(" + %4.2fX^%i ", p.coeff_tab[i], i);
                }
                printf(" + %4.2fX + %4.2f\n", p.coeff_tab[1], p.coeff_tab[0]);
            } else {
                printf(" + %4.2f\n", p.coeff_tab[0]);
            }
        }
        void sommePoly(Polynome p1 , Polynome p2 , Polynome psom)
 {
     int degsom,deg1,deg2,i=0,j=0,k=0;
     float coeffsum,coeff1,coeff2;
     Polynome *P,*S ,*Psom;
     P=&p1; S=&p2;
     degsom=max(p1.degree,p2.degree);
     psom.coeff_tab=(float*)malloc((unsigned long)(degsom+1)*sizeof (float));
     Psom=&psom;
     if( p1.degree == p2.degree)

     {
        psom.coeff_tab[k]=p1.coeff_tab[i]+p2.coeff_tab[j];
        psom.degree=p1.degree;
        Psom ++;
     i++;j++;k++;
     }
     else if(p1.degree > p2.degree) {
        psom.degree=p1.degree;
        psom.coeff_tab[k]=p1.coeff_tab[i];
        i++;k++;
    }else {
        psom.coeff_tab[k]=p2.coeff_tab[j];
        psom.degree=p2.degree;
        j++;k++;

    }
          }

Answer 1

我认为这个版本的 sommePoly 正是您正在寻找的:

void sommePoly(Polynome *p1 , Polynome *p2 , Polynome *psom)
{
        int     i;
        Polynome        *big, *sml;

        if (p1->degree > p2->degree) {
                big = p1;
                sml = p2;
        }
        else {
                big = p2;
                sml = p1;
        }

        psom->degree = big->degree;
        psom->coeff_tab = calloc(psom->degree + 1, sizeof(float));

        for (i = 0; i < sml->degree + 1; i++)
        {
                psom->coeff_tab[i] = big->coeff_tab[i] + sml->coeff_tab[i];
        }
        for (; i < big->degree + 1; i++)
        {
                psom->coeff_tab[i] = big->coeff_tab[i];
        }
}

提示 1:尝试使用 calloc() 而不是 malloc()。当尝试分配 Z 大小的 N 个项目的任何数组时，它要安全得多。 提示 2:当然，在解引用之前始终检查 calloc()/malloc() 的返回值。

为了说明 sommePoly 的预期用途:

void printPoly(Polynome *p)
{
        int     i;
        for (i = p->degree; i > 0; i--) {
                if (0.0 != p->coeff_tab[i])
                        printf("%4.2fX^%i + ", p->coeff_tab[i], i);
        }
        if (0.0 != p->coeff_tab[i])
                printf("%4.2f\n", p->coeff_tab[0]);
}

int main(int argc, char *argv[])
{
        Polynome        a, b, sum;

        a.degree = 5;
        a.coeff_tab = calloc(a.degree + 1, sizeof(float));
        a.coeff_tab[0] =  1.0;
        a.coeff_tab[1] =  8.0;
        a.coeff_tab[2] = -2.0;
        a.coeff_tab[3] =  0.0;
        a.coeff_tab[4] =  3.0;
        a.coeff_tab[5] =  1.0;

        b.degree = 3;
        b.coeff_tab = calloc(b.degree + 1, sizeof(float));
        b.coeff_tab[0] =  1.0;
        b.coeff_tab[1] = -3.0;
        b.coeff_tab[2] =  5.0;
        b.coeff_tab[3] =  7.0;

        sommePoly(&a, &b, &sum);

        printPoly(&a);
        printPoly(&b);
        printPoly(&sum);

        free(a.coeff_tab);
        free(b.coeff_tab);
        free(sum.coeff_tab);

        return 0;
}

和输出:

$ cc -g -O0 -Wall  poly.c -o poly
$ ./poly
1.00X^5 + 3.00X^4 + -2.00X^2 + 8.00X^1 + 1.00
7.00X^3 + 5.00X^2 + -3.00X^1 + 1.00
1.00X^5 + 3.00X^4 + 7.00X^3 + 3.00X^2 + 5.00X^1 + 2.00