求助一个C语言的问题

/*第一题*/
#include <stdio.h>

int main(void)
{
int i, num, index;
int a[9] = {1, 5, 7, 8, 10, 13, 16, 21};

scanf ("%d", &num);

for (i = 0; i < 9; i++)
{
if (num <= a[i])
{
index = i;
break;
}
}

for (i = 7; i >= index; i--)
a[i + 1] = a[i];

a[index] = num;

for (i = 0; i < 9; i++)
printf ("%-3d", a[i]);

return 0;
}
/*第二题*/
#include <stdio.h>

int main(void)
{
int num;
int a = 3, b = 5, c = 7;

printf ("Enter a number: ");
scanf ("%d", &num);

if (num % a == 0 && num % b == 0 && num % c == 0)
printf ("%d可以同时被3 5 7整除\n", num);
else if ((num % a == 0 && num % b == 0) || (num % a == 0 && num % c == 0) || (num % b == 0 && num % c == 0))
{
if (num % a == 0 && num % b == 0)
printf ("%d %d", a, b);
else if (num % a == 0 && num % c == 0)
printf ("%d %d", a, c);
else
printf ("%d %d", b, c);
}
else if ((num % a == 0) || (num % b == 0) || (num % c == 0))
{
if (num % a == 0)
printf ("%d", a);
else if (num % b == 0)
printf ("%d", b);
else
printf ("%d", c);
}
else
printf ("%d不能被3 5 7任何一个数整除\n");

return 0;
}

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