1 #include<stdio.h> 2 int main() 3 { 4     double number1 = 0.0; 5     double number2 = 0.0; 6     char operation = 0; 7      8     start: 9     printf("/nEnter the calculation");10     scanf("%lf %c %lf", &number1, &operation, &number2);11     12     switch(operation)13     {14         case ‘+‘:15             printf("= %lf\n",number1 + number2);16             break;17         case ‘-‘:18             printf("%lf\n", &number1 - &number2);19             break;20         case‘*‘:21             printf("%lf\n", &number1 * &number2);22             break;23         case‘/‘:24             if(number2 == 0) //check the second operand for zero25                 printf("\n\n\a Division by zero erro\n");26                 break;27             else 28                 printf("%lf\n", &number / &number2);29                 break;30         case‘%‘:31             if((long)number2 = 0;)32                 printf("\n\n\aDivision by zero erro\n");33                 break;34             else35                 printf("%lf\n", (long)number1 % (long)number2);36                 break;37         default:38             printf("\n\n\aIllegal operation\n");39             break;        40     }41     42     //The followoing statements added to prompt for continuing43     char answer = ‘n‘;44     printf("\n Do you want to do another calculation?(y or n);");45     scanf("%c", &answer);46     if(answer==‘y‘||answer == ‘y‘);47         go to start; // go back to the beginning48         49         return 0;50     51  } 

 1 /*Exercise 3.4 A calculator that allows multiple calculations */ 2 #include <stdio.h> 3  4 int main(void) 5 { 6   double number1 = 0.0;          /* First operand value a decimal number  */ 7   double number2 = 0.0;          /* Second operand value a decimal number */ 8   char operation = 0;            /* Operation - must be +, -, *, /, or %  */ 9 start:10   printf("\nEnter the calculation\n");11   scanf("%lf %c %lf", &number1, &operation, &number2);12 13   switch(operation)14   {15     case ‘+‘:                     // No checks necessary for add16       printf("= %lf\n", number1 + number2);17       break;18 19     case ‘-‘:                     // No checks necessary for subtract20       printf("= %lf\n", number1 - number2);21       break;22 23     case ‘*‘:                     // No checks necessary for multiply24       printf("= %lf\n", number1 * number2);25       break;                              26 27     case ‘/‘:28       if(number2 == 0)           // Check second operand for zero 29         printf("\n\n\aDivision by zero error!\n");30       else31         printf("= %lf\n", number1 / number2);32       break;33 34     case ‘%‘:                    // Check second operand for zero35       if((long)number2 == 0) 36          printf("\n\n\aDivision by zero error!\n");37       else38         printf("= %ld\n", (long)number1 % (long)number2);39       break;40 41     default:                     // Operation is invalid if we get to here42       printf("\n\n\aIllegal operation!\n");43       break;44   }45 46   /* The following statements added to prompt for continuing */47   char answer = ‘n‘;48   printf("\n Do you want to do another calculation? (y or n): ");49   scanf(" %c", &answer);50   if(answer == ‘y‘ || answer == ‘Y‘)51     goto start;                       /* Go back to the beginning */52 53   return 0;54 }