I'm writing a program to plot a set of cosine and sine functions, so I want to output the calculated values to a file so I can plot them with gnuplot.

Here is the code:

#include <stdio.h>
#include <math.h>

//#define PI 3.14159;

int main() {
double a1;
double x[100];
double l = 20.0;
double result[100];
int a2, n = 11;
double arg;
double PI = 3.14159;
FILE *f;
//double *ptr =
int i =0;
int j = 0;
f = fopen("output.txt", "w");
fprintf(f, "n x value");

while(n <= 100) {
a1 = n; /* To get the program to do 2 different operations for odd and even numbers
we declare 2 variables as an int and a double so when we divide them
by 2 if the value is even then a1 and a2 will be equal as integer division will
return an integer and will round and non-integer values */
a2 = n;
a1 = a1/2;
a2 = a2/2;
printf("a1 = %lf\n a2=%d\n", a1, a2);
if(a1 == a2) {
//n is even so do sine
while (i!=100) {
arg = ( ( (x[i]) * (n) * (PI) ) / (l) );
result[i] = sin(arg);
fprintf(f, "%d %lf %lf\n", n, x, result[i]); //This is the error
x[i] = x[i] +0.2;
i++;
}
}

else {

//n is odd so do cosine
while(j<=100) {
arg = ( ( (x[i]) * (n) * (PI) ) / (l) );
result[i] = cos(arg);
x[i] = x[i] +0.2;
j++;
}


}
n++;
}

fclose(f);

n++;
}

However it gets an error on line 35 - the fprintf function.

sine_and_cosine_2.c: In function ‘main’:
sine_and_cosine_2.c:35: warning: format ‘%lf’ expects type ‘double’, but argument 4 has type ‘double *’

The thing is if I try and compile this on the my universitys linux server it compiles fine as have all the times I've tried to print an array element, it's only on my laptop which runs Ubuntu 9.10 with the GCC compiler. The compiler code I use is:

gcc sine_and_cosine_2.c -lm -o sine_and_cosine_2

I'm a little bit baffled, as always help would be greatly appreciated.

Use code tags next time, so your code will be readable.

probably you meant x[i] not x as the 4'th arg to fprintf.

Aren't you lucky to have a better compiler on that Ubuntu system!

On all the others it might compile without error, but it would run incorrectly.

woot that worked, thanks for the help.

Just out of interest when it says 4th argument I thought it meant result[i] because 'f' would be the first, n the 2nd, x the 3rd and result[i] the 4th.

"%d %lf %lf\n" is the 2nd

Thanks again!