program3_11.c

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/*Example 3.11 A calculator*/
#include <stdio.h>
#include <ctype.h>

int main(void)
{
  double number1 = 0.0;          /* First operand value a decimal number  */
  double number2 = 0.0;          /* Second operand value a decimal number */
  char operation = 0;            /* Operation - must be +, -, *, /, or %  */
  char reply = 0;                /* Indicates another calculation - or not*/

  printf("\nEnter the calculation\n");
  scanf("%lf %c %lf", &number1, &operation, &number2);

  /* Code to check the input goes here */
  switch(operation)
  {
    case '+':                    /* No checks necessary for add       */
      printf("= %lf\n", number1 + number2);
      break;

    case '-':                    /* No checks necessary for subtract */
      printf("= %lf\n", number1 - number2);
      break;

    case '*':                    /* No checks necessary for multiply */
      printf("= %lf\n", number1 * number2);
      break;

    case '/':
      if(number2 == 0)           /* Check second operand for zero    */
        printf("\n\n\aDivision by zero error!\n");
      else
        printf("= %lf\n", number1 / number2);
       break;

    case '%':                    /* Check second operand for zero    */
      if((long)number2 == 0)
        printf("\n\n\aDivision by zero error!\n");
      else
        printf("= %ld\n", (long)number1 % (long)number2);
      break;

    default:                     /* Operation is invalid if we get to here */
      printf("\n\n\aIllegal operation!\n");
      break;
  }
  return 0;
}