10.29

for

#include<stdio.h>
 int main(void)
 {
     int a,n,t=0;
     printf("请输入一个数字：");
    scanf("%d",&n);
    for(a =2;a<n && t != 0;a++){
        if(n % a ==0)
        t++;
    }
    if(t == 0){
        printf("这是个质数"); 
    }else
        printf ("这不是质数");
   return 0;
}

#include<stdio.h>
int main(void)
{
    int a,b;
    for(a=2 ;a<=9;a++){
        for(b = 1;b <= 9;b++)
        printf("%d * %d =%d\n",a,b,a*b);
    }
    return 0;
}

#include<stdio.h>
int main(void)
{
    int n;
    printf("请输入边长;");
    scanf("%d",&n);
    int a;
    int b;
    for(b=1;b<=n;b++){
      for(a=1;a<=n;a++){
        printf("*");
    }
    printf("\n");
    }
    return 0;
}

#include<stdio.h>
int main(void)
{
    int n;
    printf("请输入边长;");
    scanf("%d",&n);
    int a;
    int b;
    for(b=1;b<=n;++b){
        printf("*");
    }
    printf("\n");
    for(a=1;a<=n-2;a++){
        printf("*");
      for(b=1;b<=n-2;b++){
        printf(" ");
        }
        printf("*\n");
    }
    for(b=1;b<=n;++b){
        printf("*");
    }
    return 0;
}

#include<stdio.h>
int main(void)
{
    int n;
    printf("请输入边长;");
    scanf("%d",&n);
    int a,b;
    for(a=1;a<=n;a++){
        for(b=1;b<=n;b++){
        if(a==1||a==n||b==1||b==n)
        printf("*");
        else
        printf(" ");
      }
      printf("\n");
  }
   return 0;
}