7-1：

#include <stdio.h>

#define Maxs 1001
int findmax(int a[], int N);
int main()
{
int count[Maxs] = {0};
int n;
scanf("%d", &n);

int x;
while ((scanf("%d", &x))!=EOF)
{
    count[x]++;
}

int maxi = findmax(count, n + 1);

for (int i = 0; i < n + 1; i++)
{
    if (count[maxi] == count[i])
    {
        printf("%d %d\n", i, count[i]);
    }
}

return 0;
}

int findmax(int a[], int N)
{
int maxx = 0;

for (int i = 0; i < N; i++)
{
    if (a[maxx] < a[i])
    {
        maxx = i;
    }
}

return maxx;
}

7-3：错因：只会转一圈，不会往里拐

#include <stdio.h>
#include <stdlib.h>
int main()
{
int n,ii,jj;
scanf("%d",&n);
int k=1;
int a[20][20];
int i0,i1,j0,j1,x;
i0=0;i1=n-1;
j0=0;j1=n-1;
for(x=0;x<=n/2;x++)
{
for(ii=i0,jj=j1;ii<=i1;ii++)
{
a[ii][jj]=k;
k++;
}
for(jj=j1-1,ii=i1;jj>=j0;jj--)
{
a[ii][jj]=k;
k++;
}
for(ii=i1-1,jj=j0;ii>=i0;ii--)
{
a[ii][jj]=k;
k++;
}
for(ii=i0,jj=j0+1;jj<=j1-1;jj++)
{
a[ii][jj]=k;
k++;
}
i0=i0+1,i1=i1-1,j0=j0+1,j1=j1-1;
}
for(ii=0;ii<n;ii++)
{
for(jj=0;jj<n;jj++)
printf("%4d",a[ii][jj]);
printf("\n");}

return 0;
}