Thread: Segmentation fault - won't enter for loop!

Heres my relevant bits of code:

Code:

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


#define EXPECTED_ARGS   2
#define INTEGRAL_STEPS  100
#define LOG_2           log(2) 
#define MAX_N           10


int main(int argc, char* argv[])
{
  double      integral_yn[MAX_N], recursive_yn[MAX_N];
  double      a;
  double      sum, x;
  int         valid_input;
  int         i, j, n;
  int         steps = INTEGRAL_STEPS;
  FILE       *output;

.
.
.

Code:

  /* Evaluate integral y_n */
  for(n=1; n<10; n++)
  {
    printf(" n = %d    ", n);
    integral_yn[n] = 0;
    printf("integral_yn began/n");
    for(i=0; i<steps; i++)
    {
      x = i/steps;
      sum = pow(x, n+1)/( (x + a)*steps ); 
      integral_yn[n] = integral_yn[n] + sum;
    }
    printf("integral_yn[%d] done/n", n);
  }

I reach a segmenation fault just before entering the for loop, and the line printf(" n = %d ", n); doesn't even run!

Whats wrong?

Well, I had a printf statement right before the for loop which does execute.

Here is all of my code:

Code:

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


#define EXPECTED_ARGS   2
#define INTEGRAL_STEPS  100
#define LOG_2           log(2) 
#define MAX_N           10


int main(int argc, char* argv[])
{
  double      integral_yn[MAX_N], recursive_yn[MAX_N];
  double      a;
  double      sum, x;
  int         valid_input;
  int         i, j, n;
  int         steps = INTEGRAL_STEPS;
  FILE       *output;


  /* Get command line input */
  if(argc == EXPECTED_ARGS)
  {
    valid_input = sscanf(argv[1], "%lf", &a);
    printf("a stored\n");
  }
  else
  {
    printf("***Enter program name followed by a strictly positive number***\n");
    valid_input = 0;
  }


  /* Checks a strictly positive */
  if(a <= 0)
  {
    printf("***Number must be strictly positive***\n");
    valid_input = 0;
  }


  /* Final validation */
  if(!valid_input)
  {
    printf("Input validation failed!!!\n");
    return(EXIT_FAILURE);
  }


  /* Evaluate y_1 using integral */
  double y1 = 1 - a*LOG_2;


  integral_yn[0] = y1;
  printf("integral_yn[0] done\n");
  recursive_yn[0] = y1;
  printf("recursive_yn[0] done\n");


  /* Evaluate integral y_n */
  for(n=1; n<10; n++)
  {
    printf(" n = %d    ", n);
    integral_yn[n] = 0;
    printf("integral_yn began/n");
    for(i=0; i<steps; i++)
    {
      x = i/steps;
      sum = pow(x, n+1)/( (x + a)*steps ); 
      integral_yn[n] = integral_yn[n] + sum;
    }
    printf("integral_yn[%d] done/n", n);
  }

Sorry for the length. The line printf("recursive_yn[0] done\n"); does print, but the next one does not - I get a segmentation fault

is there something wrong with this line?

Code:

     integral_yn[n] = integral_yn[n] + sum;

No seg fault here either. You do have a logic problem on line 70 though. i / steps always equals 0.

Lolz. I'm just a little wary about giving putting my whole assignment on the internet. I'll get screwed if one of my classmates copies it and corrects the error. I'll put the code up later though, I'm on my phone.

I don't understand why i / steps always equals 0 though, i goes from 0 to 99 and steps = 100 right?

Oh wait, it's because i and steps are int!

Full code:

Code:

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


#define EXPECTED_ARGS   2
#define INTEGRAL_STEPS  100
#define LOG_2           log(2) 
#define MAX_N           10


int main(int argc, char* argv[])
{
  double      integral_yn[MAX_N], recursive_yn[MAX_N];
  double      a;
  double      sum, x;
  int         valid_input;
  int         i, j, n;
  int         steps = INTEGRAL_STEPS;
  FILE       *output;


  /* Get command line input */
  if(argc == EXPECTED_ARGS)
  {
    valid_input = sscanf(argv[1], "%lf", &a);
    printf("a stored\n");
  }
  else
  {
    printf("***Enter program name followed by a strictly positive number***\n");
    valid_input = 0;
  }


  /* Checks a strictly positive */
  if(a <= 0)
  {
    printf("***Number must be strictly positive***\n");
    valid_input = 0;
  }


  /* Final validation */
  if(!valid_input)
  {
    printf("Input validation failed!!!\n");
    return(EXIT_FAILURE);
  }


  /* Evaluate y_1 using integral */
  double y1 = 1 - a*LOG_2;


  integral_yn[0] = y1;
  printf("integral_yn[0] done\n");
  recursive_yn[0] = y1;
  printf("recursive_yn[0] done\n");


  /* Evaluate integral y_n */
  for(n=1; n<10; n++)
  {
    printf(" n = %d    ", n);
    integral_yn[n] = 0;
    printf("integral_yn began/n");
    for(i=0; i<steps; i++)
    {
      x = i/steps;
      sum = pow(x, n+1)/( (x + a)*steps ); 
      integral_yn[n] = integral_yn[n] + sum;
    }
    printf("integral_yn[%d] done/n", n);
  }
  printf("integral_yn done/n");
  /* Evaluate recursive y_n */
  for(j=1; j<10; j++)
  {
    recursive_yn[j] = 1/(j+1) - a*recursive_yn[j-1];
  }
  printf("recursive_yn done/n");
  /* Prints to file assign4.out */
  output = fopen("assign4.out", "w");


  fprintf(output, "a = %.4lf, y_1 = %.6lf\n", a, integral_yn[0]);
  
  for(i=1; i++; i<10)
  {
    fprintf(output, "%10.9lf   %10.9lf", integral_yn[i], recursive_yn[i]);
  }


  fclose(output);
  return(0);
}

Code:

printf("integral_yn began/n");

The above is wrong "/n" should be "\n".

Tim S.