printf problem

I would like to know how to replace the text inside the "printf"statement with a variable which is a double.

Code:

#include <stdio.h>

int main(void)
{
   /* redirect standard output to a file */
   if (freopen("OUTPUT.txt", "w", stdout)
       == NULL)
      fprintf(stderr, "error redirecting stdout\n");

   /* this output will go to a file */
   printf("This will go into a file.");

   /* close the standard output stream */
   fclose(stdout);

   return 0;
}

its ungent thanks

Hmm, ungent? Do you mean urgent? Uh-oh...

Hmm, printf()=C, not C++, right?

Hmm, how about

Code:

printf("%d", myDouble);

I don't know much printf, so d might me the wrong watchyamacallit?

printf("%f", myDouble);

EDIT - and C is a subset of C++ so it's all good

how would you put a real number in c++ in a variable inside the printf statement.

C++ uses cout...

Code:

cout<<myDouble;

I think printf is deprecated in C++, I didnt touch it Cos I start with C++, lol~

also how do you add a blank space using printf(); and what would be the statement for if it was an integer instead.

Originally posted by niroopan
also how do you add a blank space using printf();

you must be missing the basic concept of printf here. printf takes your format string and inserts the variables you give it in to it where the various % codes are. so to print a double

printf ("%f", mydouble);

to print a double with a space after it

printf ("%f ", mydouble);

also, you really shouldnt be using freopen here, theres no need to. just use

fprintf (myfile, "%f ", mydouble);

(that is after you fopen() myfile of course)

Code:

double foo=3.14127;
printf("the value of foo is %f",foo);
printf("  ");
printf("which also happens to be the value of PI\n");
// or to put it all together

printf("the value of foo is %f  which also happens to be the value of PI\n",foo);

the real code is this,

Code:

//Author: Gavinn Niroopan//
//Program Name: ngsummary.h//
//Revision Date: 2002-10-11//
//Explanation: to use variables and loopibf structures display a summary,the following assignment will demonstrate a program structure, code layout and use logic structure//

#include <iostream.h>	//allows cout statement//
#include <iomanip.h>   	//allows decimal formatting, setiosflags()//
#include <conio.h>     	//allows clrscr() and getch()//
#include <string.h>    	//allows strcpy()//
#include <time.h>      	//allows the call of time function//
#include <stdio.h>      //allows printf statement//

int main(void)
{
	int studcountmax, year;
   double term1, term2, studaverage, classtotal;

   time_t t=time(NULL); //time function//
								//Fowler Statement//
   setiosflags(ios::right|ios::fixed);
   							//Will display the time//
   cout <<setw(79)<<ctime(&t)<<endl;
   cout<<setw(79)<<"Gavinn Niroopan"<<endl;
   cout<<setw(79)<<"2002-10-11"<<endl;
   cout<<setw(79)<<"Mr. Slack"<<endl;
   cout<<setw(79)<<"ICS 3MO-A"<<endl;
   gotoxy(32,8); 			//moves cursor to location (x,y) on screen//
   cout<<"Summary Program"<<endl;
   gotoxy(32,9);
   cout<<"~~~~~~~~~~~~~~~"<<endl;
   							//"for" loop for spacing//
   	for(int i= 1;i <=6;i++)
      	cout<<endl;
   cout<<"Explanation:"<<endl;
	cout<<"~~~~~~~~~~~"<<endl<<endl;
   cout<<"\tTo create a program which will use variables and looping structures"<<endl;
   cout<<"\tto display a summary sheet. The following assignment will demonstrate"<<endl;
   cout<<"\ta program structure, code layout and use logic structures. The program"<<endl;
   cout<<"\tThe program will use data derived from the user and date acquired from"<<endl;
   cout<<"\the system at time of execution."<<endl;

   getch();					//Pause screen//
   clrscr();				//clear screen//

   cout<<ctime(&t)<<endl<<endl;
   gotoxy(29,4);
   cout<<"Class Summary Analysis"<<endl;
   gotoxy(29,5);
   cout<<"~~~~~~~~~~~~~~~~~~~~~~"<<endl<<endl;
   cout<<"\tHow many students are being processed:     ";
   cin>>studcountmax;
   cout<<"\tWhat school year is being processed:       ";
   cin>>year;

   clrscr();				//clear screen//

   for(int studcount=1;studcount<=studcountmax;studcount++)
   	{
   		cout<<ctime(&t)<<endl<<endl;
   		gotoxy(26,4);
   		cout<<"Student Term Evaluation Record"<<endl;
   		gotoxy(26,5);
   		cout<<"~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~"<<endl<<endl;
   		cout<<"\t\tEnter the 1st term mark: - ";
   		cin>>term1;
         cout<<"\t\tEnter the 2nd term mark: - ";
         cin>>term2;

         studaverage = (term1 + term2)/2;
         classtotal = classtotal + studaverage;

   	   // redirect standard output to a file //
   		if (freopen("OPEN.txt", "a", stdout)== NULL)

      		fprintf(stderr, "error redirecting stdout\n");

   		//this output will go to a file //
         {
         printf("Student ",studcount,"%f",studaverage);
         cout<<endl;
         }

         // close the standard output stream //
         fclose(stdout);
         clrscr();
     	}



   getch();

   return 0;
}

I want it to look like this in the txt file;

student 1 63.00%
student 2 78.00%

etc. but its not working properly.

stop using freopen.
and do something like this (code may not be 100% accurate)

fout << "Student " << studcount << studaverage << '%' << endl;

or with fprintf

fprintf (myfile "Student %i %.2f%%\n", studcount, studaverage);

why redirect stdout when you could use fopen or fstream classes which would make this a piece of cake.
On the whole its probably not a good idea to mix c and c++ i/o routines. stick to one or the other.

Code:

fprintf (myfile "Student %i %.2f%%\n", studcount, studaverage);

how and where would you write the line in my code and how would i write to filename as open.txt instead of myfile.

you mean to say you know how to use freopen() but not fopen()????

Originally posted by niroopan
the real code is this,

Code:

//Author: Gavinn Niroopan//
//Program Name: ngsummary.h//
//Revision Date: 2002-10-11//
//Explanation: to use variables and loopibf structures display a summary,the following assignment will demonstrate a program structure, code layout and use logic structure//

#include <iostream.h>	//allows cout statement//
#include <iomanip.h>   	//allows decimal formatting, setiosflags()//
#include <conio.h>     	//allows clrscr() and getch()//
#include <string.h>    	//allows strcpy()//
#include <time.h>      	//allows the call of time function//
#include <stdio.h>      //allows printf statement//

int main(void)
{
	int studcountmax, year;
   double term1, term2, studaverage, classtotal;

   time_t t=time(NULL); //time function//
								//Fowler Statement//
   setiosflags(ios::right|ios::fixed);
   							//Will display the time//
   cout <<setw(79)<<ctime(&t)<<endl;
   cout<<setw(79)<<"Gavinn Niroopan"<<endl;
   cout<<setw(79)<<"2002-10-11"<<endl;
   cout<<setw(79)<<"Mr. Slack"<<endl;
   cout<<setw(79)<<"ICS 3MO-A"<<endl;
   gotoxy(32,8); 			//moves cursor to location (x,y) on screen//
   cout<<"Summary Program"<<endl;
   gotoxy(32,9);
   cout<<"~~~~~~~~~~~~~~~"<<endl;
   							//"for" loop for spacing//
   	for(int i= 1;i <=6;i++)
      	cout<<endl;
   cout<<"Explanation:"<<endl;
	cout<<"~~~~~~~~~~~"<<endl<<endl;
   cout<<"\tTo create a program which will use variables and looping structures"<<endl;
   cout<<"\tto display a summary sheet. The following assignment will demonstrate"<<endl;
   cout<<"\ta program structure, code layout and use logic structures. The program"<<endl;
   cout<<"\tThe program will use data derived from the user and date acquired from"<<endl;
   cout<<"\the system at time of execution."<<endl;

   getch();					//Pause screen//
   clrscr();				//clear screen//

   cout<<ctime(&t)<<endl<<endl;
   gotoxy(29,4);
   cout<<"Class Summary Analysis"<<endl;
   gotoxy(29,5);
   cout<<"~~~~~~~~~~~~~~~~~~~~~~"<<endl<<endl;
   cout<<"\tHow many students are being processed:     ";
   cin>>studcountmax;
   cout<<"\tWhat school year is being processed:       ";
   cin>>year;

   clrscr();				//clear screen//

   for(int studcount=1;studcount<=studcountmax;studcount++)
   	{
   		cout<<ctime(&t)<<endl<<endl;
   		gotoxy(26,4);
   		cout<<"Student Term Evaluation Record"<<endl;
   		gotoxy(26,5);
   		cout<<"~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~"<<endl<<endl;
   		cout<<"\t\tEnter the 1st term mark: - ";
   		cin>>term1;
         cout<<"\t\tEnter the 2nd term mark: - ";
         cin>>term2;

         studaverage = (term1 + term2)/2;
         classtotal = classtotal + studaverage;

   	   // redirect standard output to a file //
   		if (freopen("OPEN.txt", "a", stdout)== NULL)

      		fprintf(stderr, "error redirecting stdout\n");

   		//this output will go to a file //
         {
         printf("Student ",studcount,"%f",studaverage);
         cout<<endl;
         }

         // close the standard output stream //
         fclose(stdout);
         clrscr();
     	}



   getch();

   return 0;
}

I want it to look like this in the txt file;

student 1 63.00%
student 2 78.00%

etc. but its not working properly.

what are those braces supposed to be enclosing? there's no loop or conditional starting there