Question

write a C++ program that reads in a text file and reads each character or lexemes and states what token it is and writes to another file

for example:

while (fahr < upper) a = 23.00 whileend

Output:

token lexeme

--------------------------------

keyword while

separator (

identifier fahr

operator <

identifier upper

separator )

identifier a

operator =

real 23.00

keyword whileend

the program aslo reads in comments but does not add to the list. characters that are commented out or pseudocode is not counted

Answer 1

#include <iostream>
#include <string.h>
using namespace std;

bool isDelimiter(char ch)
{
   if (ch == ' ' || ch == '+' || ch == '-' || ch == '*' ||
       ch == '/' || ch == ',' || ch == ';' || ch == '>' ||
       ch == '<' || ch == '=' || ch == '(' || ch == ')' ||
       ch == '[' || ch == ']' || ch == '{' || ch == '}')
       return (true);
   return (false);
}

// Returns 'true' if the character is an OPERATOR.
bool isOperator(char ch)
{
   if (ch == '+' || ch == '-' || ch == '*' ||
       ch == '/' || ch == '>' || ch == '<' ||
       ch == '=')
       return (true);
   return (false);
}

bool isSeparator(char ch)
{
if(ch=='(' || ch==')')
{
return true;
}
return false;
}

// Returns 'true' if the string is a VALID IDENTIFIER.
bool validIdentifier(char* str)
{
   if (str[0] == '0' || str[0] == '1' || str[0] == '2' ||
       str[0] == '3' || str[0] == '4' || str[0] == '5' ||
       str[0] == '6' || str[0] == '7' || str[0] == '8' ||
       str[0] == '9' || isDelimiter(str[0]) == true)
       return (false);
   return (true);
}

// Returns 'true' if the string is a KEYWORD.
bool isKeyword(char* str)
{
   if (!strcmp(str, "if") || !strcmp(str, "else") ||
       !strcmp(str, "while") || !strcmp(str, "do") ||
       !strcmp(str, "break") ||
       !strcmp(str, "continue") || !strcmp(str, "int")
       || !strcmp(str, "double") || !strcmp(str, "float")
       || !strcmp(str, "return") || !strcmp(str, "char")
       || !strcmp(str, "case") || !strcmp(str, "char")
       || !strcmp(str, "sizeof") || !strcmp(str, "long")
       || !strcmp(str, "short") || !strcmp(str, "typedef")
       || !strcmp(str, "switch") || !strcmp(str, "unsigned")
       || !strcmp(str, "void") || !strcmp(str, "static")
       || !strcmp(str, "struct") || !strcmp(str, "goto"))
       return (true);
   return (false);
}

// Returns 'true' if the string is an INTEGER.
bool isInteger(char* str)
{
   int i, len = strlen(str);

   if (len == 0)
       return (false);
   for (i = 0; i < len; i++) {
       if (str[i] != '0' && str[i] != '1' && str[i] != '2'
           && str[i] != '3' && str[i] != '4' && str[i] != '5'
           && str[i] != '6' && str[i] != '7' && str[i] != '8'
           && str[i] != '9' || (str[i] == '-' && i > 0))
           return (false);
   }
   return (true);
}

// Returns 'true' if the string is a REAL NUMBER.
bool isRealNumber(char* str)
{
   int i, len = strlen(str);
   bool hasDecimal = false;

   if (len == 0)
       return (false);
   for (i = 0; i < len; i++) {
       if (str[i] != '0' && str[i] != '1' && str[i] != '2'
           && str[i] != '3' && str[i] != '4' && str[i] != '5'
           && str[i] != '6' && str[i] != '7' && str[i] != '8'
           && str[i] != '9' && str[i] != '.' ||
           (str[i] == '-' && i > 0))
           return (false);
       if (str[i] == '.')
           hasDecimal = true;
   }
   return (hasDecimal);
}

// Extracts the SUBSTRING.
char* subString(char* str, int left, int right)
{
   int i;
   char* subStr = (char*)malloc(
               sizeof(char) * (right - left + 2));

   for (i = left; i <= right; i++)
       subStr[i - left] = str[i];
   subStr[right - left + 1] = '\0';
   return (subStr);
}

// Parsing the input STRING.
void parse(char* str)
{
   int left = 0, right = 0;
   int len = strlen(str);
   string outputStr = "";

   while (right <= len && left <= right) {
       if (isDelimiter(str[right]) == false)
           right++;

       if (isDelimiter(str[right]) == true && left == right) {
           if (isOperator(str[right]) == true)
           {
               printf("operator %c\n", str[right]);
           }
           else if(isSeparator(str[right])==true){
           printf("separator %c\n", str[right]);
           }

           right++;
           left = right;
       } else if (isDelimiter(str[right]) == true && left != right
               || (right == len && left != right)) {
           char* subStr = subString(str, left, right - 1);

           if (isKeyword(subStr) == true)
               printf("keyword %s\n", subStr);

           else if (isInteger(subStr) == true)
               printf("integer %s\n", subStr);

           else if (isRealNumber(subStr) == true)
               printf("real %s\n", subStr);

           else if (validIdentifier(subStr) == true
                   && isDelimiter(str[right - 1]) == false)
               printf("identifier %s\n", subStr);

           left = right;
       }
   }
   return;
}

int main()
{

  
  
  
   ifstream inFile;
char str[100] = "while (fahr < upper) a = 23.00 whileend";
//To read the data from the file uncomment the below code and add inputFile.txt in working directory.
// inFile.open("inputFile.txt");
// if (!inFile) {
// cout << "Unable to open file";
// exit(1); // terminate with error
// }
  
// while (inFile >> x) {
// str = str + x;
// }
  
   parse(str);

   return (0);
}

Output:

keyword while
separator (
identifier fahr
operator <
identifier upper
separator )
identifier a
operator =
real 23.00
identifier whileend