Questin about files

Hi!!!I have a question...How can I use the data of a file???
For example at the following code:

Code:

#include <stdio.h>
int main()
{
FILE *fp;
int i,n;
fp = fopen("d.dat","w");
if (fp==NULL) {
    exit(0);
}
for (i=0; i<=10; i++){
	 printf("Give number:");
	 scanf("%d",&n);
	 fprintf(fp,"%d,%d\n",n,i*n);
}	   
fclose(fp);
return 0;
}

I want to write a function that finds the max of the numbers i*n,that exist in the file "d.dat"...How can I do this????

 

open the file using "w+" so you can write and read from it. After your write operation finishes, rewind the stream so that you can read its data.

Code:

for(...)
{
   fprintf(...)
}

rewind(fp);
fseek(fp, 0, SEEK_SET); // same as rewind but w/o resetting eof bits

while(fscanf(fp, "%d", &n) == 1)
   // do something with n

As for a function, you could probably pass in a second parameter by reference indicating the max number in the file.

Code:

void findMax(int curval, int *curmax)
{
    if(curval > *curmax)
        *curmax = curval;
}

In the read back of the file

Code:

int n, some_max = 0;
...
// loop for adding to file
...
while(fscanf(...) == 1)
    findMax(n, &some_max);

Maybe something like that

You are aware that the contents of the file get over written each time the program is run using "w" or "w+"?? If that's a problem, then create the file first and open it using "r+' or "a+".

 

Moved to C Programming from Introduction.