Просмотр исходного текста страницы C/Small Application/Calculator

==A calculator that allows multiple calculations==



   
<source lang="cpp">
#include <stdio.h>
int main()
{
  double number1 = 1.0;
  double number2 = 2.0;
  char operation = "+";
  char answer = 0;

  switch(operation)
  {
    case "+":
      printf("= %lf\n", number1 + number2);
      break;
    case "-":
      printf("= %lf\n", number1 - number2);
      break;
    case "*":
      printf("= %lf\n", number1 * number2);
      break;
    case "/":
      if(number2 == 0)
        printf("\n\n\aDivision by zero error!\n");
      else
        printf("= %lf\n", number1 / number2);
      break;
    case "%":
      if((long)number2 == 0)
        printf("\n\n\aDivision by zero error!\n");
      else
        printf("= %ld\n", (long)number1 % (long)number2);
      break;
    default:
      printf("\n\n\aIllegal operation!\n");
  }
}

           
       </source>


==An improved calculator==



   
<source lang="cpp">
/*
Beginning C, Third Edition
 By Ivor Horton
 ISBN: 1-59059-253-0
 Published: Apr 2004
 Publisher: apress
*/
/*  */
#include <stdio.h>       /* Standard input/output                    */
#include <string.h>      /* For string functions                     */
#include <ctype.h>       /* For classifying characters               */
#include <stdlib.h>      /* For converting strings to numeric values */
#include <math.h>        /* For power() function                     */
void main()
{
   char input[256];        /* Input expression                  */
   char number_string[30]; /* Stores a number string from input */
   char op = 0;            /* Stores an operator                */
  unsigned int index = 0; /* Index of the current a character in input */
  unsigned int to = 0;    /* To index for copying input to itself      */         
  size_t input_length = 0; /* Length of the string in input      */  
  unsigned int number_length = 0; /* Length of the string in number_string */
  double result = 0.0;            /* The result of an operation        */        
  double number = 0.0;            /* Stores the value of number_string  */
   printf("\nTo use this calculator, enter any expression with"
                                           " or without spaces");
   printf("\nAn expression may include the operators:");
   printf("\n           +, -, *, /, %%, or ^(raise to a power).");
   printf("\nUse = at the beginning of a line to operate on ");
   printf("\nthe result of the previous calculation.");
   printf("\nUse quit by itself to stop the calculator.\n\n");
   /* The main calculator loop */
   while(strcmp(gets(input), "quit") != 0)
   {
     input_length = strlen(input);     /* Get the input string length */
     /* Remove all spaces from the input by copy the string to itself */
     /* including the string terminating character                    */
     for(to = 0, index = 0 ; index<=input_length ; index++)
     if(*(input+index) != " ")          /* If it is not a space  */
       *(input+to++) = *(input+index);  /* Copy the character    */
     input_length = strlen(input);  /* Get the new string length */
     index = 0;                    /* Start at the first character */
    if(input[index]== "=")    /* Is there =?         */
      index++;                /* Yes so skip over it */
    else
    {                         /* No - look for the left operand */
      /* Look for a number that is the left operand for the 1st operator */
      /* Check for sign and copy it */
      number_length = 0;      /* Initialize length      */
      if(input[index]=="+" || input[index]=="-")             /* Is it + or -?  */
        *(number_string+number_length++) = *(input+index++); /* Yes so copy it */ 
      /* Copy all following digits */
      for( ; isdigit(*(input+index)) ; index++)           /* Is it a digit? */           
       *(number_string+number_length++) = *(input+index); /* Yes - Copy it  */   
      /* copy any fractional part */
      if(*(input+index)==".")             /* Is it decimal point? */                    
      { /* Yes so copy the decimal point and the following digits */
        *(number_string+number_length++) = *(input+index++);  /* Copy point */
        for( ; isdigit(*(input+index)) ; index++)         /* For each digit */         
          *(number_string+number_length++) = *(input+index);     /* copy it */ 
      }
      *(number_string+number_length) = "\0";    /* Append string terminator */
      /* If we have a left operand, the length of number_string */
      /* will be > 0. In this case convert to a double so we    */
      /* can use it in the calculation                          */
      if(number_length>0)
        result = atof(number_string);  /* Store first number as result */        
    }
     /* Now look for "op number" combinations */
     for(;index < input_length;)
     { 
       op = *(input+index++);     /* Get the operator */
       /* Copy the next operand and store it in number */
       number_length = 0;    /* Initialize the length  */
       /* Check for sign and copy it */
       if(input[index]=="+" || input[index]=="-")          /* Is it + or -?  */           
       *(number_string+number_length++) = *(input+index++); /* Yes - copy it. */ 
       /* Copy all following digits */
       for( ; isdigit(*(input+index)) ; index++)      /* For each digit */           
       *(number_string+number_length++) = *(input+index);   /* copy it. */   
       /* copy any fractional part */
       if(*(input+index)==".")               /* Is is a decimal point? */
       { /* Copy the  decimal point and the following digits */
         /* Copy point     */
         *(number_string+number_length++) = *(input+index++);  
         for( ; isdigit(*(input+index)) ; index++)      /* For each digit */          
           *(number_string+number_length++) = *(input+index); /* copy it. */ 
       }
       *(number_string+number_length) = "\0";   /* terminate string */              
  
       /* Convert to a double so we can use it in the calculation */
       number = atof(number_string);
       /* Execute operation, as "result op= number" */
       switch(op)
       {  
          case "+":      /* Addition        */
            result += number;
            break;
          case "-":      /* Subtraction     */
            result -= number;
            break;
          case "*":      /* Multiplication  */
            result *= number;
            break;
          case "/":      /* Division         */
            /* Check second operand for zero */
            if(number == 0)   
              printf("\n\n\aDivision by zero error!\n");
            else
              result /= number;
            break;
          case "%":      /* Modulus operator - remainder  */
            /* Check second operand for zero */
            if((long)number == 0)               
              printf("\n\n\aDivision by zero error!\n");
            else
              result = (double)((long)result % (long)number);
            break;
          case "^":      /* Raise to a power              */
            result = pow(result, number);
            break;
          default:       /* Invalid operation or bad input */
            printf("\n\n\aIllegal operation!\n");
       } 
     }
     printf("= %f\n", result);  /* Output the result */
   }
}

           
       </source>