Question

我正在编写一个程序，用于使用结构和指针查找两个有理数的加法，乘法和除法。我在使用指针输入数字时遇到问题。我的代码应该如何纠正？谢谢！

#include <stdio.h>
struct rational
{
    int nu;
    int de;
}*p1,*p2,*p3;
void add()
{
    p1->nu = p1->nu*p2->de + p1->de*p2->nu;
    p3->de = p1->de * p2->de;
    printf("%d\n--\n%d\n",p3->nu,p3->de);
}
void multiply()
{
    p3->nu = p1->nu * p2->nu;
    p3->de = p1->de * p2->de;
    printf("%d\n--\n%d\n",p3->nu,p3->de);
}
void divide()
{
    p3->nu = p1->nu * p2->de;
    p3->de = p1->de * p2->nu;
    printf("%d\n--\n%d\n",p3->nu,p3->de);
}
int main()
{
    int a,b,c,d,choice;
    printf("Enter the first rational number.\n");
    scanf("%d%d",&a,&b);
    p1->nu = a;
    p1->de = b;
    printf("Enter the second rational number.\n");
    scanf("%d%d",&c,&d);
    p2->nu = c;
    p2->de = d;
    scanf("%d",&choice);
    switch (choice)
    {
        case 1: add();
                break;
        case 2: multiply();
                break;
        case 3: divide();
                break;
    }
    return 0;
}

Answer 1

您永远不会初始化指针，因此您提供的代码正在调用未定义的行为。在实际使用p1之前，p2和p3使它们指向某个现有对象，或者为它们动态分配内存。

Answer 2

E.g。

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

struct rational{
    int nu;
    int de;
} ;

int main(void){
    int n, d;
    struct rational *p;

    p=(struct rational*)malloc(sizeof(struct rational));
    printf("Enter the rational number.\n");
/*  Indirection
    scanf("%d/%d", &n, &d);
    p->nu = n;
    p->de = d;
*/
scanf("%d/%d", &p->nu, &p->de);//Direct
    printf("%d/%d\n", p->nu, p->de);
    return 0;
}

Answer 3

解决。我在struct rational中声明了3 p1个变量：p2，p3和main()。然后我将这些变量的地址导出到有三个指针作为原型的函数中。

#include <stdio.h>  
struct rational
{
    int nu;
    int de;
};
void add(struct rational *p1,struct rational *p2,struct rational *p3)
{
    p3->nu = (p1->nu)*(p2->de) + (p1->de)*(p2->nu);
    p3->de = p1->de * p2->de;
    printf("%d\n-\n%d\n",p3->nu,p3->de);
}
void multiply(struct rational *p1,struct rational *p2,struct rational *p3)
{
    p3->nu = p1->nu * p2->nu;
    p3->de = p1->de * p2->de;
    printf("%d\n-\n%d\n",p3->nu,p3->de);
}
void divide(struct rational *p1,struct rational *p2,struct rational *p3)
{
    p3->nu = p1->nu * p2->de;
    p3->de = p1->de * p2->nu;
    printf("%d\n-\n%d\n",p3->nu,p3->de);
}
int main()
{
    struct rational p1,p2,p3;

    int a,b,c,d,choice;
    printf("Enter the first rational number.\n");
    scanf("%d/%d", &p1.nu, &p1.de);
    printf("Enter the second rational number.\n");
    scanf("%d/%d", &p2.nu, &p2.de);
    printf("1. Addition 2. Multiplication 3. Division: ");
    scanf("%d",&choice);
    switch (choice)
    {
        case 1: add(&p1,&p2,&p3);
                break;
        case 2: multiply(&p1,&p2,&p3);
                break;
        case 3: divide(&p1,&p2,&p3);
                break;
    }
    return 0;
}
//Output
//Enter the first rational number.
//3/4
//Enter the second rational number.
//7/9
//1. Addition 2. Multiplication 3. Division: 1
//55
//-
//36

使用指针向结构成员输入值

3 个答案: