How to use fprintf for writing data to a file

Question

I want to write data from a C program to a file, so that Excel can read the file to plot a graph of the data. But I'm not sure of the exact syntax to use for fprintf. I have stdlib.h declared in the very top of my program. I declared "File *fp;" in main but I'm getting that File and fp are undeclared. What could be the problem?

**EDIT: My program compiles and runs but now my output file doesn't contain any data This is what I have at the end of a while loop that does some computations..

 fp = fopen( "out_file.txt", "w" ); // Open file for writing

 fprintf(fp, "x = %f, y = %f, vx = %f, vy = %f, time = %f, ", x,y,vx,vy,time);

Answer 1

Your logic should look something like this:

fp = fopen( "out_file.txt", "w" ); // Open file for writing

while ( some condition )
{

    ... some calculations

    fprintf(fp, "x = %f, y = %f, vx = %f, vy = %f, time = %f, ", x,y,vx,vy,time);
}

fclose(fp);