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:

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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:

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cout<<myDouble;

---

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

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

Quote:

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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:

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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()???? :confused:

Quote:

---

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

Quote:

---

Originally posted by black
I think printf is deprecated in C++, I didnt touch it Cos I start with C++, lol~:D

---

No...C++ fully supports the C std libs.....

A few changes may be made on a C++ implementation, but the interface should be the same....

printf is legal...yay!