C program is unable to give correct output

[Ujagar]

I have written a small program in C but I don't really understand why my program does not work. Here is my code:

#include <stdio.h>
#include <math.h>
void main(void)
{
FILE *outFile;
float p[1000];
float lambda = 1.0e-3;
float i;
int j;
int m = 2;
outFile=fopen("myfile.txt","w");
for (i=0.1; i < 1.0; i+=0.1)
{
for (j=0; j<=1000; j++)
{
p[0]=1.0e-5;
p[j+1]=p[j] + lambda * pow((p[j]),(m/2)) * pow(i,m);
fprintf(outFile, "\n%lf\n",i,j,p[j+1]);
}
}
fclose(outFile);
}

But the generated output is not satisfactory. What and where is the problem? For example i need to print out the value of i, j and p[j+1]. and the iterations seem wrong. It suppose to come out like this:

(example answer only)

i j p[j+1]

0.1 1 1.0002e-5
0.1 2 1.0003e-4
.
.
0.2 1 1.0005e-4
.
.
.
1 1000 1.011e-2

One more thing: is it possible for me to draw this number into line chart/graph with the help of above program?

[kelfro]

There are few bugs in your code, some of which include:

1. Your inner FOR loop is buggy since it is resulting into stack corruption:

for (j=0; j<=1000; j++)
{
p[0]=1.0e-5;
p[j+1]=p[j] + lambda * pow((p[j]),(m/2)) * pow(i,m);
fprintf(outFile, "\n%lf\n",i,j,p[j+1]);
}

2. The below line of code simply prints/saves the variable i onto your outFile.

fprintf(outFile, "\n%lf\n",i,j,p[j+1]);

[Ujagar]

If that's the equation that I need to use without changing it, is there any other way to do that?

p[j+1]=p[j] + lambda * pow((p[j]),(m/2)) * pow(i,m);

Thanks for your reply.

[kelfro]

What I'm saying is that array "p" is having 1000 elements. These elements are indexed from 0 to 999. If your FOR loop goes up to this j<=1000 value then at some point you will reach p[999+1]=p[999] and then p[1000+1]=p[1000] which implies array out of bounds. Atmost your loop will be able to go to and stay withing the bounds of the array is 998. So at most you will have p[998+1]=p[998] and the loop should then stop. Do you understand what I mean?

[!const]

In other words you don't need to have so big array on the stack. You could even store those values to heap. I mean you can have something like this:

float *temp = new float[1000];