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Implement a scanner or lexical analyzer in C programming assignment help

The assignment deals with implementing a program to read a file written in a predefined grammar and scan all the tokens within it using C. The program designed by our C programming assignment helpers reads the file and goes line by line, scanning for all the available tokens building a symbol table that is printed on the screen. The number of tokens that belong to different classes is also calculated.

Reading and Scanning Tokens in C

#include #include #include #include /* enumeration of the token classes */ enum {KEYWORD,IDENTIFIER,INTEGER,REAL,SPECIAL}; /* definition of a token for the token table */ typedef struct { char token[128]; /* token found */ int class; /* class to which this token belongs */ int count; /* number of times the token appears */ }token_t; token_t token_table[256]; /* token table */ int n_tokens; /* number of tokens in the table */ /*function to determine if the character c is a digit, returns 1 if it's a digit and 0 otherwise */ int is_digit(char c) { return (c>='0' && c<='9'); } /*function to determine if the character c is a character, returns 1 if it's a character and 0 otherwise */ int is_character(char c) { return (c>='a' && c<='z') || (c>='A' && c<='Z'); } /* function to determine if character c is a special char, returns 1 if it's a special character, 0 otherwise */ int is_special(char c) { return (c=='(' || c==')' || c=='[' || c==']' || c=='+' || c=='-' || c=='=' || c==',' || c==';'); } /* Function to determine if the string identifier is a keyword returns 1 if it's a keyword and 0 otherwise */ int is_keyword(char *identifier) { if(!strcmp(identifier,"IF")) return 1; if(!strcmp(identifier,"THEN")) return 1; if(!strcmp(identifier,"ELSE")) return 1; if(!strcmp(identifier,"BEGIN")) return 1; if(!strcmp(identifier,"END")) return 1; return 0; } /* scanner is the function that goes through all character in the file and builds a table of tokens */ void scanner(FILE *input) { int c; int state; char token[128]; int pos; enum {START,IDENTIFIER,INTEGER,REAL}; /* indicate the state we are in */ state=START; n_tokens=0; while(!feof(input)) { c=getc(input); /* read a char from the file */ switch(state) { case START: pos=0; if(is_digit(c)) { state=INTEGER; token[pos++]=c; } else if(is_character(c)) { state=IDENTIFIER; token[pos++]=toupper(c); } else if(is_special(c)) { token_table[n_tokens].token[0]=c; /* copy symbol character to table */ token_table[n_tokens].token[1]='\0'; /* add an end of string */ token_table[n_tokens].class=SPECIAL; n_tokens++; /* increment number of tokens in table */ } break; case INTEGER: if(is_digit(c)) { state=INTEGER; token[pos++]=c; } else { if(c=='.') { token[pos++]=c; /* save point in token */ state=REAL; } else { token[pos++]='\0'; /* add an end of string */ strcpy(token_table[n_tokens].token,token); /* save token in table */ token_table[n_tokens].class=INTEGER; /* save class of token */ n_tokens++; /* increment number of tokens in table */ state=START; ungetc(c,input); /* reuse current character */ } } break; case REAL: if(is_digit(c)) { state=REAL; token[pos++]=c; } else { token[pos++]='\0'; /* add an end of string */ strcpy(token_table[n_tokens].token,token); /* save token in table */ token_table[n_tokens].class=REAL; /* save class of token */ n_tokens++; /* increment number of tokens in table */ state=START; ungetc(c,input); /* reuse current character */ } break; case IDENTIFIER: if(is_character(c)) { state=IDENTIFIER; token[pos++]=toupper(c); } else { token[pos++]='\0'; /* add an end of string */ strcpy(token_table[n_tokens].token,token); /* save token in table */ if(is_keyword(token)) token_table[n_tokens].class=KEYWORD; /* save class of token */ else token_table[n_tokens].class=IDENTIFIER; /* save class of token */ n_tokens++; /* increment number of tokens in table */ state=START; ungetc(c,input); /* reuse current character */ } break; } } } int main(int argc,char **argv) { FILE *file; int i,j; int class_count[5]={0,0,0,0,0}; /* count for each class, initialize to zero */ token_t table[256]; /* token table with unique entries */ int n_unique=0,found; if(argc!=2) { printf("Missing source filename.\n"); printf("Usage:\n\tscanner \n"); exit(1); } file=fopen(argv[1],"rt"); if(file==NULL) { printf("Error opening the file %s\n",argv[1]); exit(1); } scanner(file); /* scan the file and fill the token table */ fclose(file); printf("\nToken Table: \n"); printf("\n%-10s %s\n","TOKEN","CLASS"); printf("----------------------\n"); for(i=0; i