Question

2. Write a C program that reads characters from a text file, and recognizes the identifiers in the text file. It ignores the rest of the characters. An identifier is a sequence of letters, digits, and underscore characters, where the first character is always a letter or an underscore character. Lower and upper case characters can be part of the identifier. The recognized identifier are copied into the output text.

b. Change the C program in exercise 2, so that all identifiers include only upper case letters. So, if the input file includes the identifier _abCd1_9t the output file will include the corresponding identifier _ABCD1_9T

Answer 1

Here is the C code for the first problem (i.e. Copying all identifiers to output.txt file) :

#include <stdbool.h> #include <stdio.h> #include <string.h> #include <stdlib.h> // Returns 'true' if the character is a DELIMITER. 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 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); } // 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);  while (right <= len && left <= right) {           if (isDelimiter(str[right]) == false)                   right++;                if (isDelimiter(str[right]) == true && left == right) { right++;                        left = right;           } else if (isDelimiter(str[right]) == true && left != right || (right == len && left != right)) {                       char* subStr = subString(str, left, right - 1); if (validIdentifier(subStr) == true && isDelimiter(str[right - 1]) == false)                    { FILE *fptr; fptr = fopen("output.txt", "w"); fgets(sentence, sizeof(sentence), stdin); fprintf(fptr, "%s", str); fclose(fptr); } left = right;                }       }       return; } // DRIVER FUNCTION int main() {       // maximum legth of string is 100 here  char str[100] = "int a = b + 1c; "; char filename[20]; printf("Enter the file name : ",filename); scanf("%s",filename); FILE * fp = fopen(filename, "r"); if (fp == NULL) return 1;     char c; char buf[10];   while(fscanf(fp, "%s", buf) != EOF)     {               if(c == ' ' || c == '\n')                continue;              else parse(buf);        }       fclose(fp);     return (0); }

Here is the C code for the second problem (i.e. Copying all identifiers to output.txt file in the uppercased form) :

#include <stdbool.h> #include <stdio.h> #include <string.h> #include <stdlib.h> // Returns 'true' if the character is a DELIMITER. 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 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); } // 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);  while (right <= len && left <= right) {           if (isDelimiter(str[right]) == false)                   right++;                if (isDelimiter(str[right]) == true && left == right) { right++;                        left = right;           } else if (isDelimiter(str[right]) == true && left != right || (right == len && left != right)) {                       char* subStr = subString(str, left, right - 1); if (validIdentifier(subStr) == true && isDelimiter(str[right - 1]) == false)                    { for(i=0; str[i]!='\0'; i++) if(str[i]>='a' && str[i]<='z') str[i] = str[i] - 32; FILE *fptr; fptr = fopen("output.txt", "w"); fgets(sentence, sizeof(sentence), stdin); fprintf(fptr, "%s", str); fclose(fptr); } left = right;                 }       }       return; } // DRIVER FUNCTION int main() {       // maximum legth of string is 100 here  char str[100] = "int a = b + 1c; "; char filename[20]; printf("Enter the file name : ",filename); scanf("%s",filename); FILE * fp = fopen(filename, "r"); if (fp == NULL) return 1;     char c; char buf[10];   while(fscanf(fp, "%s", buf) != EOF)     {               if(c == ' ' || c == '\n')                continue;              else parse(buf);        }       fclose(fp);     return (0); }