Question

我尝试实现中文余数定理，为此我应该找到一些数的乘法逆。函数正常工作，但如果它在while循环后工作，则会产生错误的结果。

#include<stdio.h>
#include<stdlib.h>
#include<string.h>    
main(){
    int rem[5],div[5],fac[5];
    int t = 0;
    int c = 0;
    int m = 1;
    int d = 0;
    void inverse(int,int);
    //take remainder and divider from user
    while ((rem[t] != -1)  & (div[t] != -1))
    {
        printf("Enter remainder and divider in an order(-1 -1 to finish):");
        scanf_s("%d" "%d", &rem[t], &div[t]);
        if (rem[t] != -1 & div[t] != -1)
            t++;
        else {
            printf("You ask to stop! Thank you.\n");
            div[t] = -1;
            rem[t] = -1;
        }
    }

    while ((div[c] != -1) & (rem[c] != -1)) {/* print until face null character */
        printf("%d . character is %d and %i\n", c + 1,rem[c], div[c]);
        m = m*div[c];
        c++;
    }
    printf(" m is %d\n", m);

    //implement crt algorithm
    while ((div[d] != -1) & (rem[d] != -1)) {
        fac[d] = m/div[d];
        printf(" m(%d) is %d\n",d+1, fac[d]);
        inverse(div[d], fac[d]);
        d++;
    }

    inverse(5,21);//this lines works if I first enter -1 -1 
    inverse(7,15);
    system("pause");
    //return 0;
}
//this is for finding gcd and inverse
int a, b, i;
int k = 1;
int q[10];
int r[10];
int x[10];
int y[10];

void inverse(int a, int b){
    q[1] = (a / b);
    r[1] = a%b;
    q[0] = a;
    r[0] = b;
    //find gcd of two numbers
    while (r[k] != 0){
        k = k++;
        q[k] = r[k - 2] / r[k - 1];
        r[k] = r[k - 2] % r[k - 1];
    }
    printf("gcd of %d and %d is: %d\n", a, b, r[k - 1]);
    //check whether these two numbers are relatively prime,if it is then find inverse
    if (r[k - 1] != 1)
        printf("These two numbers should be relatively prime\n");
    else{
        x[k - 1] = -q[k - 1];
        y[k - 1] = 1;
        i = k - 1;

        while (i > 1){
        x[i - 1] = -x[i] * q[i - 1] + y[i];
        y[i - 1] = x[i];
        i = i - 1;
        }
        //check whether the inverse of number is less than 0, if it is then add the modulo
        if ((x[1] % a) < 0)
        printf("multiplicative inverse of %d in mod %d is %d\n", b, a, (x[1] % a) + a);

        else
        printf("multiple inverse of %d in mod %d is %d\n", b, a, x[1] % a);

    }
}

Answer 1

我看到的主要问题是在全局范围内使用int k = 1;。如果您在逆方法（k）内初始化k = 1，则无法继续引用先前的计算。

另外，我不确定C语义，但在Java k = k++;中实际上不会增加k。您可能只想要k++。

inverse函数正常工作，但如果在while循环后工作则会产生错误的答案

1 个答案: