Integers and Arithmetic Operations

1. We can use the / operator for the division and the % operator for the remainder:

   import std.stdio;
   
   void main() {
       int first;
       write("Please enter the first number: ");
       readf(" %s", &first);
   
       int second;
       write("Please enter the second number: ");
       readf(" %s", &second);
   
       int quotient = first / second;
       int remainder = first % second;
   
       writeln(first, " = ",
               second, " * ", quotient, " + ", remainder);
   }
   

2. We can determine whether the remainder is 0 or not with an if statement:

   import std.stdio;
   
   void main() {
       int first;
       write("Please enter the first number: ");
       readf(" %s", &first);
   
       int second;
       write("Please enter the second number: ");
       readf(" %s", &second);
   
       int quotient = first / second;
       int remainder = first % second;
   
       // We cannot call writeln up front before determining
       // whether the remainder is 0 or not. We must terminate
       // the line later with a writeln.
       write(first, " = ", second, " * ", quotient);
   
       // The remainder must be printed only if nonzero.
       if (remainder != 0) {
           write(" + ", remainder);
       }
   
       // We are now ready to terminate the line.
       writeln();
   }
   

3. import std.stdio;
   
   void main() {
       while (true) {
           write("0: Exit, 1: Add, 2: Subtract, 3: Multiply,",
                 " 4: Divide - Please enter the operation: ");
   
           int operation;
           readf(" %s", &operation);
   
           // Let's first validate the operation
           if ((operation < 0) || (operation > 4)) {
               writeln("I don't know this operation");
               continue;
           }
   
           if (operation == 0){
               writeln("Goodbye!");
               break;
           }
   
           // If we are here, we know that we are dealing with
           // one of the four operations. Now is the time to read
           // two integers from the user:
   
           int first;
           int second;
   
           write(" First number: ");
           readf(" %s", &first);
   
           write("Second number: ");
           readf(" %s", &second);
   
           int result;
   
           if (operation == 1) {
               result = first + second;
   
           } else if (operation == 2) {
               result = first - second;
   
           } else if (operation == 3) {
               result = first * second;
   
           } else if (operation == 4) {
               result = first / second;
   
           }  else {
               writeln(
                   "There is an error! ",
                   "This condition should have never occurred.");
               break;
           }
   
           writeln("       Result: ", result);
       }
   }
   

4. import std.stdio;
   
   void main() {
       int value = 1;
   
       while (value <= 10) {
           if (value != 7) {
               writeln(value);
           }
   
           ++value;
       }
   }