//11) Write a C program that prompts the user to choose an operation to do on 2 input integers. The
                //operations are addition, subtraction, multiplication, and division. Note: the program should not allow the division by zero.
                #include<stdio.h>
                operation();
                int main()
                {   int x,y,op;
                    printf("enter integer number of x:");
                    scanf("%d",&x);
                    printf("enter integer number of y:");
                    scanf("%d",&y);
                    printf("choose an operation:\n1 to addition\n2 to subtraction\n3 to multiplication\n4 to division\n");
                    scanf("%d",&op);
                    if(op==4)
                    {
                        if(y==0)
                        {
                            printf("the program not allow the division by zero");
                            return ;
                        }
                        else
                            printf("%d",operation(x,y,op));
                    }
                    else
                        printf("%d",operation(x,y,op));
                }
                int operation(int x ,int y, int op)
                {   switch(op)
                    {
                        case 1:
                            return x+y;
                            break;
                        case 2:
                            return x-y;
                            break;
                        case 3:
                            return x*y;
                            break;
                        case 4:
                            return x/y;
                            break;
                        default:
                            printf("choose from 1 to 4");
                    }
                }

                //--------------------------------------------------------------------------------------------------

                //12) Write a C program that will print the following pattern:
                #include<stdio.h>
                char fun();
                int main()
                {
                    int rows,i,k;
                    scanf("%d",&rows);
                    for(i=rows ; i>=1 ;i--)
                    {
                        for(k=i;k>=1;k--)
                            printf("%c",fun());
                        printf("\n");
                    }
                }
                char fun()
                {
                    return '*';
                }

                //--------------------------------------------------------------------------------------------------

                //13) Write a C program that will print the following pattern:
                #include<stdio.h>
                char fun()
                {
                    return '*';
                }
                int main()
                {
                    int rows,i,l,s;
                    printf("enter number of rows:");
                    scanf("%d",&rows);
                    s=rows*2;
                    for(i=1 ; i<=s ;i+=2)
                    {
                        for(l=1; l<=i ;l++)
                            printf("%c",fun());
                        printf("\n");
                    }

                    int k,m;
                    for(k=s;k>=1;k-=2)
                    {
                        for(m=k-1;m>=1;m--)
                            printf("%c",fun());
                        printf("\n");
                    }
                }

                //--------------------------------------------------------------------------------------------------

                //14) Write a C program that finds the sum of the first n natural numbers
                #include<stdio.h>
                int sum(int n)
                {
                    int sum=0;
                    for(int i=1;i<=n;i++)
                    {
                        sum+=i;
                    }
                    return sum;
                }
                int main()
                {
                    int n;
                    printf("enter value of n:");
                    scanf("%d",&n);
                    printf("the sum of the first n natural numbers: %d",sum(n));
                }

                //--------------------------------------------------------------------------------------------------

                //15) Write a C code that finds the sum of the digits of a number.
                #include<stdio.h>
                int sumofdigits(int n)
                {   int z,sum=0;
                    while(n!=0)
                    {
                        z=n%10;
                        sum+=z;
                        n/=10;
                    }
                    return sum;
                }
                int main()
                {
                    int n;
                    printf("enter number of n:");
                    scanf("%d",&n);
                    printf("the sum of the digits of a number: %d",sumofdigits(n));
                }