HTML output

calc.c

/*

  CALC.C
  ======
  (c) Paul Griffiths
  Email: mail@paulgriffiths.net

  Simple CGI web-based calculator

*/


#include <stdlib.h>
#include <stdio.h>
#include <math.h>
#include "cgihelp.h"


/*  Global macros  */

#define ERR_NO_VALUE              (1)
#define ERR_BAD_VALUE             (2)
#define ERR_ZERO_DIVIDE           (3)
#define ERR_BAD_OPERATOR          (4)


/*  main() function  */

int main() {
    int   a, b, result, error = 0;
    char *num1, *num2, *op, *endptr = NULL;


    /*  Output HTML header  */

    printf("Content-Type: text/html\n\n");
    
    printf("<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.0//EN\">\n\n");
    printf("<HTML>\n\n");

    printf("<HEAD>\n");
    printf("    <TITLE>CGI Calculator</TITLE>\n");
    printf("</HEAD>\n\n");

    printf("<BODY>\n\n");
    printf("<H1>CGI Calculator</H1>\n\n");


    /*  Get input and process it  */
    
    if ( InitInput(100) ) {
	printf("<P>ERROR: Problem getting input</P>\n\n");
    }
    else {
	printf("<P>Last result: ");

	num1 = GetValue("number1");
	num2 = GetValue("number2");
	op   = GetValue("operator");
	    
	if ( !num1 && !num2 && !op )
	    printf("No previous calculation.</P>\n\n");
	else {

	    /*  Get first number  */

	    if ( !num1 )
		error = ERR_NO_VALUE;
	    else {
		a = strtol(num1, &endptr, 0);
		if ( *endptr )
		    error = ERR_BAD_VALUE;
	    }


	    /*  Get second number  */

	    if ( !num2 ) 
		error = ERR_NO_VALUE;
	    else {
		b = strtol(num2, &endptr, 0);
		if ( *endptr )
		    error = ERR_BAD_VALUE;
	    }


	    /*  Get operator and calculate result  */

	    if ( !op )
		error = ERR_NO_VALUE;
	    else {
		if ( !strcmp(op, "plus") )
		    result = a + b;
		else if ( !strcmp(op, "minus") )
		    result = a - b;
		else if ( !strcmp(op, "multiplied by") )
		    result = a * b;
		else if ( !strcmp(op, "divided by") )
		    if ( b )
			result = a / b;
		    else
			error = ERR_ZERO_DIVIDE;
		else if ( !strcmp(op, "to the power of") )
		    result = pow(a, b);
		else
		    error = ERR_BAD_OPERATOR;
	    }


	    /*  Check for input errors and output result  */

	    switch ( error ) {
	    case ERR_NO_VALUE:
		printf("Error - one or more values are missing.</P>\n\n");
		break;
		
	    case ERR_BAD_VALUE:
		printf("Error - one or more values was invalid.</P>\n\n");
		break;
		
	    case ERR_ZERO_DIVIDE:
		printf("Error - can't divide by zero.</P>\n\n");
		break;
		
	    case ERR_BAD_OPERATOR:
		printf("Error - invalid operator.</P>\n\n");
		break;
		
	    default:
		printf("%d %s %d = %d</P>\n\n", a, op, b, result);
		break;
	    }
	    
	}

	printf("<BR><HR><BR>\n\n");


	/*  Output calculator form  */

	printf("<FORM ACTION=\"/cgi-bin/calc\" METHOD=\"GET\">\n");
	printf("<TABLE BORDER=\"1\" CELLPADDING=\"10\">\n");
	printf("    <TR>\n");
	printf("        <TH>First number</TH>\n");
	printf("        <TH>Operator</TH>\n");
	printf("        <TH>Second number</TH>\n");
	printf("    </TR>\n\n");
	printf("    <TR>\n");
	printf("        <TD><INPUT TYPE=\"text\" NAME=\"number1\" SIZE=\"8\"></TD>\n");
	printf("        <TD><SELECT NAME=\"operator\">\n");
	printf("            <OPTION>plus</OPTION>\n");
	printf("            <OPTION>minus</OPTION>\n");
	printf("            <OPTION>multiplied by</OPTION>\n");
	printf("            <OPTION>divided by</OPTION>\n");
	printf("            <OPTION>to the power of</OPTION>\n");
	printf("        </SELECT></TD>\n");
	printf("        <TD><INPUT TYPE=\"text\" NAME=\"number2\" SIZE=\"8\"></TD>\n");
	printf("    </TR>\n\n");
	printf("    <TR>\n");
	printf("        <TD COLSPAN=\"3\"><CENTER>");
	printf("<INPUT TYPE=\"submit\" VALUE=\"Calculate!\">");
	printf("</CENTER></TD>\n");
	printf("    </TR>\n");
	printf("</TABLE>\n");
	printf("</FORM>\n\n");

	printf("</BODY>\n\n</HTML>\n");
    }


    /*  Clean up and exit  */
 
    FreeCGI();
    return EXIT_SUCCESS;
}

cgihelp.h

/*

  CGIHELP.H
  =========
  (c) Paul Griffiths 1999
  Email: mail@paulgriffiths.net

  Interface to CGI helper functions

*/


#ifndef PG_CGIHELP
#define PG_CGIHELP


/*  Global macros  */

#define ERR_BADREQUEST          (1)
#define ERR_BADMALLOC           (2)


/*  Function declarations  */

int    InitInput      (int   maxbuffer);
char * GetValue       (char *key);
char * GetIndexedValue(int   index);
char * GetIndexedKey  (int   index);
void   FreeCGI        ();


#endif    /*  PG_CGIHELP  */

cgihelp.c

/*

  CGIHELP.C
  =========
  (c) Paul Griffiths 1999
  Email: mail@paulgriffiths.net

  CGI helper functions

*/


#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include "cgihelp.h"


/*  Forward function declarations  */

void cleanurl(char *str);


/*  Linked list node to hold key/value pairs  */

typedef struct varlist {
    char *key;
    char *value;
    struct varlist *next;
} varlist;

varlist* varstart;


/*  Get all key/value pairs from input  */

int InitInput(int maxbuffer) {
    varlist *var;
    char    *input;


    /*  Allocate memory for input buffer  */

    if ( !(input = malloc(sizeof(char) * maxbuffer)) )
	return ERR_BADMALLOC;
    memset(input, '\0', sizeof(char) * maxbuffer);


    /*  Determine request method and fill input buffer  */
    
    if ( !strcmp(getenv("REQUEST_METHOD"), "GET") )
	strncpy(input, getenv("QUERY_STRING"), maxbuffer - 1);
    else if ( !strcmp(getenv("REQUEST_METHOD"), "POST") )
	fgets(input, maxbuffer, stdin);
    else
	return ERR_BADREQUEST;


    /*  Allocate memory for first key/value pair  */

    if ( ! (varstart = malloc(sizeof(varlist)) ) )
	return ERR_BADMALLOC;
    var = varstart;

    
    /*  Populate key/value pairs  */

    if ( (input = strtok(input, "=")) ) {
	while ( var ) {
	    if ( !(var->key = malloc(sizeof(char) * strlen(input))) )
		return ERR_BADMALLOC;
	    strcpy(var->key, input);
	    cleanurl(var->key);

	    input = strtok(NULL, "&");
	    if ( !(var->value = malloc(sizeof(char) * strlen(input))) )
		return ERR_BADMALLOC;
	    strcpy(var->value, input);
	    cleanurl(var->value);

	    if ( (input = strtok(NULL, "=")) ) {
		if ( !(var->next = malloc(sizeof(varlist))) )
		    return ERR_BADMALLOC;
	    }
	    else {
		var->next = NULL;
	    }
	    var = var->next;
	}
    }	 
    else {

	/*  No key/value pairs in input if we get here  */

	free(varstart);
	varstart = NULL;
    }

    free(input);
    return 0;
}


/*  Retrieves a value from a key  */

char * GetValue(char *key) {
    varlist *var = varstart;
    while ( var ) {
	if ( !strcmp(key, var->key) )
	    return var->value;
	var = var->next;
    }
    return NULL;
}


/*  Retrieves a key using a 1-based index  */

char * GetIndexedKey(int index) {
    int n;
    varlist *var = varstart;
    for ( n = 1; n < index; ++n )
	if ( var->next == NULL )
	    return NULL;
	else
	    var = var->next;
    return var->key;
}


/*  Retrieves a value using a 1-based index  */

char * GetIndexedValue(int index) {
    int n;
    varlist *var = varstart;
    for ( n = 1; n < index; ++n )
	if ( var->next == NULL )
	    return NULL;
	else
	    var = var->next;
    return var->value;
}


/*  Frees memory used by key/value pairs  */

void FreeCGI() {
    varlist *var = varstart;
    while ( var ) {
	free(var->key);
	free(var->value);
	var = var->next;
	free(varstart);
	varstart = var;
    }
}


/*  Cleans up url-encoded string  */
	
void cleanurl(char *str) {
    char asciinum[3] = {0};
    int i = 0, c;
    
    while ( str[i] ) {
	if ( str[i] == '+' )
	    str[i] = ' ';
	else if ( str[i] == '%' ) {
	    asciinum[0] = str[i+1];
	    asciinum[1] = str[i+2];
	    str[i] = strtol(asciinum, NULL, 16);
	    c = i+1;
	    do {
		str[c] = str[c+2];
	    } while ( str[2+(c++)] );
	}
	++i;
    }
}

Please send all comments, suggestions, bug reports etc to mail@paulgriffiths.net