Writing out an array using fprintf

Question

I'm having trouble writing an array of double numbers in a text file. The problem is, the code runs, but doesn't write out anything.

 #include <stdio.h>
 #include <stdlib.h>

 int main() {

     FILE *out;
     double numbers[30];
     int i=0;

     for(i;i<30;i++) 
         scanf("%lf", &numbers[i]);

     out=fopen("out.txt", "w");

     if (out == NULL) {

         fprintf(stderr, "error in opening .txt");
         exit(EXIT_FAILURE);
     }

     while ( i<30 ) {

         fprintf(out, "%.3f", numbers[i]);
         i++;
     }

     fclose(out);

     return 0;
 }

Basically, the code is supposed to write out an array of 30 double numbers in a text file, and round the decimals to '.3'.

Use a` for` - Better than a while loop in this case. Reset i. Use braces around scanf and check the return value — Ed Heal
– Ed Heal, Commented Mar 21, 2015 at 11:28

shauryachats · Accepted Answer · 2015-03-21 11:30:26Z

4

You forgot to re-initialise i to 0, hence the current value of i is 30, which effectively causes the while loop to not execute.

 i = 0; //Re-initialise i.
 while ( i<30 ) {

         fprintf(out, "%.3f", numbers[i]);
         i++;
     }

It would be better, if you use a for loop, as it's syntax helps you to remember to initialise the increment variable.

for (i = 0; i < 30; ++i)
     fprintf(out, "%.3f", numbers[i]);

answered Mar 21, 2015 at 11:30

shauryachats

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