输出孪生素数的程序

Question

我需要编写一个输入数字的代码，然后检查给定数字是否为跟随它的素数的孪生素数。以下是我到目前为止的情况：

int isPrime (int Value){
    int Number;
        for (Number=2; Number <= Value-1; Number++){
        if (Value % Number ==0)
            return 0;
        else
            return 1;
}
}
int nextPrime(int current){
    while (1){
    if (isPrime(current))
        return current;
        current++;
    }
}
int main(){
    int a;
    int First = nextPrime (a);
    int Second = nextPrime(First + 1);
    scanf("%d", &a);
    if (Second - First == 2) {
        printf("%d and %d are twin primes.", First, Second);
    } else {
        printf("%d and %d are not twin primes.", First, Second);
    }
    return 0;
}

Answer 1

第一次调用a时，nextPrime(a)未初始化。要获取除未定义行为之外的任何内容，您需要在调用scanf之前读取输入值，以便将其值初始化为用户的输入：

int a;
int First;
int Second;

scanf("%d", &a); /* move this line before the nextPrime calls */
First = nextPrime (a);
Second = nextPrime(First + 1);