Loop Timing Changes Considerably

[randtekk]

Trying to teach myself C/ANSI C. I have been playing with the code below. The first iteration using the limit values of -1000 and +1000, the program takes about 2 seconds to perform the processing. I can then try it again, without exiting the program, using the same values, and it is almost instantaneous, even though the number of calculations performed does not change. What is the reason for the time difference between the first, and subsequent iterations?

  // Training 4.cpp : Defines the entry point for the console application.
//
#include "stdafx.h"
#include <stdio.h>
#include "time.h"
//#include <stdbool.h>
//validate that input is integer
int get_int(void);
//validate that range limits are valid
bool bad_limits(int begin, int end, int low, int high);
// calculate the sum of the squares of the integers
// a through b
double sum_squares(int a, int b);

int main(void)
{
    const int MIN = -1000;   // lower limit to range
    const int MAX = 1000;  // upper limit to range
    int start;                         // start of range
    int stop;                          // end of range
    double answer;
	time_t startime, stoptime;
    printf("This program computes the sum of the squares of "
                "integers in a range. \nThe lower bound should not "
               "be less than -1000 and\nthe upper bound should not "
               "be more than 1000.\nEnter the limits (enter 0 for "
               "both limits to quit.):\nLower Limit: ");
    start = get_int();
    printf("Upper Limit: ");
    stop = get_int();
    while (start !=0 || stop !=0)
    {

        if (bad_limits(start, stop, MIN, MAX))
             printf("Please Try Again.\n");
        else
            {
				startime=time(NULL);
                 answer = sum_squares(start, stop);
				 stoptime=time(NULL);
				 printf("\nTime Lapsed %f seconds.\n\n", difftime(stoptime, startime));
                 printf("The sum of the squares of the integers ");
                 printf("from %d to %d is %g\n", start, stop, answer);

            }
          printf("Enter the limits (enter 0 for both to exit):\n");
          printf("Lower Limit: ");
          start = get_int();
          printf("Upper Limit: ");
          stop = get_int();

    }

    printf("Done. \n");
    return 0;

}

int get_int(void)
{
    int input;
    char ch;

    while (scanf("%d" , &input) != 1)
    {
          while ((ch = getchar()) != '\n')
              putchar(ch); // dispose of bad input
          printf(" is not an integer. \nPlease enter an integer value");

    }
    return input;
}

double sum_squares(int a, int b)
{
    double total = 0;
    int i;
  //  for (i = a, i <= b, i++)

	for(i = a; i <= b; i++ )
	{
	        total += i * i;
			printf("%d %0.1f\n", i, total);
	}
    return total;

}

bool bad_limits(int begin, int end, int low, int high)
{
    bool not_good = false;
    if (begin > end)
    {
        printf("%d is not smaller that %d. \n", begin, end);
        not_good  = true;

    }
    
    if (begin < low || end < low)
    {
        printf("Values must be %d or greater.\n", low);
        not_good  = true;
    }

    if (begin > high || end > high)
    {
        printf("Values must be %d or lower.\n",high);
        not_good  = true;
    }
    
    return not_good;
    
}

[SamuelAdams]

When you run a program, the results stay in memory until that memory is needed for something else. When you exit the program, chances are it flushes memory so the first time it takes longer.

[jlb]

Trying to teach myself C/ANSI C.

Come into the modern world, learn ISO C instead. Use a compiler that complies to the most current C standard. The current standard for Programming Language C (C11) is ISO/IEC 9899:2011, published 2011-12-08.

[randtekk]

Thank you SamuelAdams and jlb for your replies.

jlb: I plan to for my own personal benefit, however, right now I am working to learn to program PSoC controllers for a local prototyping firm, and they (PSoC Controllers) use ANSI C.

http://www.cypress.com/documentation/development-kitsboards/cy8ckit-044-psoc-4-m-series-pioneer-kit