Calculator

                       /*Bismillahir Rahmanur Rahim*/
//Template created by topcoder00

# include <stdio.h>
# include <math.h>
using namespace std;

int choice;
void start()
{
printf ("Instruction to use calculator\n");
printf ("Press 0 for Addition\n");
printf ("Press 1 for Subtraction\n");
printf ("Press 2 for Multipication\n");
printf ("Press 3 for Division\n");
printf ("Press 4 for Modulus\n");
printf ("Press 5 for Power\n");
printf ("Press 6 for Factrolial\n");
printf ("Press 7 for And Oparation\n");
printf ("Press 8 for Or Oparation\n");
printf ("Press 9 for Xor Oparation\n");
printf ("Press -1 for Exit\n");
}

void add()
{
    double a,b;printf("Give two numbers with space.\n");
    scanf("%lf %lf",&a,&b);
    printf("%.2lf",a+b);
}
void sub()
{
    double a,b;printf("Give two numbers with space.\n");
    scanf("%lf %lf",&a,&b);
    printf("%.2lf",a-b);
}
void mul()
{
    double a,b;printf("Give two numbers with space.\n");
    scanf("%lf %lf",&a,&b);
    printf("%.2lf",a*b);
}
void div()
{
    double a,b;printf("Give two numbers with space.\n");
    again:
    scanf("%lf %lf",&a,&b);
    if(b==0){printf("2nd number cann't be 0. Please re-enter two numbers.\n");goto again;}
    printf("%.2lf",a/b);
}
void mod()
{
    int a,b;printf("Give two numbers with space.\n");
    again:
    scanf("%d %d",&a,&b);
    if(b==0){printf("2nd number cann't be 0. Please re-enter two numbers.\n");goto again;}

    printf("%d",a % b);
}
void power()
{
    double a,b;printf("Give two numbers with space.\n");
    scanf("%lf %lf",&a,&b);
    printf("%.2lf",pow(a,b));
}
void fact()
{
    int a;printf("Give the number.\n");
    scanf("%d",&a);
    int m=1;
    for(int i=1;i<=a;i++)
    {
        m*=i;
    }
    printf("%d",m);
}
void andop()
{
    int a,b;printf("Give two numbers with space.\n");
    scanf("%d %d",&a,&b);
    printf("%d",a & b);
}
void orop()
{
    int a,b;printf("Give two numbers with space.\n");
    scanf("%d %d",&a,&b);
    printf("%d",a | b);
}
void xorop()
{
    int a,b;printf("Give two numbers with space.\n");
    scanf("%d %d",&a,&b);
    printf("%d",a ^ b);
}

int main()
{
    start();
    printf("Choose an option\n");
    again:
    scanf("%d",&choice);

    switch(choice)
    {
        case 0:
        add();break;
        case 1:
        sub();break;
        case 2:
        mul();break;
        case 3:
        div();break;
        case 4:
        mod();break;
        case 5:
        power();break;
        case 6:
        fact();break;
        case 7:
        andop();break;
        case 8:
        orop();break;
        case 9:
        xorop();break;
        case (-1):
        return 0;
        default:
        printf("Wrong entry. Please give your choice\n");
        goto again;
    }
    printf("\n\nAgain choice an option\n\n");
    goto again;
    cout<<"\n\n\n\n\n\n\nDesigned by Iftekhar ahmed eather,\nStudent of CSE (07 batch),\nBUBT, Mirpur";
    return 0;
}