12.Hollow rectangle

 

Steps

• First we will count the number of lines i.e 9
• So i will iterate from 1 to n // n is the value given by user for number of lines
• Now for inner loop j we need to see how many times the pattern is printed i.e 15
• Let it be m
• So j will iterate from 1 to m 
• Now we need to see where stars are printed and where space is printed
• First we can see for the first line (horizontal) and last line (horizontal)
• These two conditions will be i==1 for first line and i==n for last line
• Next we see that each time first star is printed and last star is printed (vertical)
• These two conditions will be j==1 for first vertical line and j==m for last line
• These four conditions can be used together using logical or 
• It will be used in a if  condition inside j loop
• True part will print * 
• False part will print space
• Remember to add "\n"

Code

#include<stdio.h>

#include<conio.h>

void main(){

int i,j,n,m;

clrscr();

printf("Enter number of rows ");

scanf("%d",&n);

printf("Enter number of columns");

scanf("%d",&m);

for(i=1;i<=n;i++)

    {

          for(j=1;j<=m;j++)

               {

                    if(i==1 || i ==n || j==1 || j==m)

                          {

                               printf("*");

                            }

                    else 

                           {

                            printf(" ");    

                             }   

                   }

           printf("\n");

     }

getch();

}

Note: scanf is used for taking user input