The Timing is incorret

All these times should be the same:
Total Time Duration0.841 ms
Total Time Duration2.384 ms
Total Time Duration0.4 ms
Total Time Duration0.411 ms
Total Time Duration0.411 ms
Total Time Duration0.55 ms
Total Time Duration0.411 ms
Total Time Duration0.401 ms
Total Time Duration0.41 ms
Press any key to continue

What am I doing wrong?

Code:

---

#include< iostream >
#include< iomanip >
#include< cstdlib >
#include< ctime >
#include< cstdio >
#include< fstream >

const int vSize = 3;
using namespace std;



int main()
{
 
    int vec[vSize]={5000, 5000, 5000};//,50000//,100000,200000,400000};

    //Declare the clock variables
    clock_t start,finish, start1, finish1, start2, finish2;
    clock_t startAll;

    //Declare and initialize all the variables
  double duration, duration1, duration2;
   
    //Declare the streams and the input and output files
    ifstream inFile;
  ofstream outFile;

    inFile.open("input1.txt");
  outFile.open("A:/output1.txt");

   
int Sum=0;
   
   
   
    for (int iterationcountselector = 0; iterationcountselector < vSize; ++iterationcountselector)
    {
        start=clock();
        for(int i =0; i < vec[iterationcountselector] ; i++)
        {
              Sum++;
              outFile<< Sum<<endl;
        }
   

    /*    finish=clock();
        duration=(double)(finish-start)/CLOCKS_PER_SEC;
        cout<<"          "<< setw(4)<< duration;*/
       
   
          finish=clock();
        duration=(double)(finish-start)/CLOCKS_PER_SEC;
        cout<<"Total Time Duration"<< duration<<" ms"<< endl;

    }
    for (iterationcountselector = 0; iterationcountselector < vSize; ++iterationcountselector)
    {
       
    start1=clock();
        for(int i =0; i < vec[iterationcountselector]; i++)
        {
             
              Sum++;
              outFile<< Sum<<endl;
        }
   

          finish1=clock();
        duration1=(double)(finish1-start1)/CLOCKS_PER_SEC;
        cout<<"Total Time Duration"<< duration1<<" ms"<< endl;
    }

for (iterationcountselector = 0; iterationcountselector < vSize; ++iterationcountselector)
    {
       
    start2=clock();
        for(int i =0; i < vec[iterationcountselector]; i++)
        {
             
              Sum++;
              outFile<< Sum<<endl;
        }
   

          finish2=clock();
        duration2=(double)(finish2-start2)/CLOCKS_PER_SEC;
        cout<<"Total Time Duration"<< duration2<<" ms"<< endl;
    }


    return 0;
}//end of main

---

What makes you think that your process has 100% of the CPU time during the entire time the program is running? Operating systems may interupt a program during its run to perform necessary tasks. When the OS is done with whatever it needed to do, the program will be restarted. This happens many times each second but it is transparent to you the user. Depending on where in your programs execution the OS decided to switch to another task and what specific tasks the OS needed to accomplish at that time, your timing values are bound to differ by varying amounts as is apparent in your results mentioned. For all of those loops to perform in the exact same amount of time, you would at least need to ensure that your program would be the only thing running from start to finish.

and (if what I remember is correct) interrupt signals are sent to your program to pause it and make it wait for the devices to continue. I believe they are known as IRQs. (or its the other way around when the software sends an IRQ to the hardware, I forgot...)

edit:
ok just checked it out:
IRQs are sent form the hardware to the CPU so the CPU stops communication with the program (for like a nanosec) and talks with the hardware etc.

-LC

>>Total Time Duration2.384 ms
>>Total Time Duration0.4 ms

You can't legally call that "variation", Salem ;)

It's off by 600%.

Code:

---

#include< iostream >
#include< iomanip >
#include< ctime >
#include< fstream >

const int vSize = 6;
using namespace std;



int main()
{
   
        int vec[vSize]={300, 500, 700,900, 1200, 1300};

        //Declare the clock variables
        clock_t start,finish, start1, finish1, start2, finish2, start3, finish3,
                start4, finish4, start5, finish5;
//        clock_t startAll;

        //Declare and initialize all the variables
    double duration, duration1, duration2, duration3, duration4, duration5=0;
       
    //Declare the streams and the input and output files
       
    ofstream outFile;
    ofstream outFile2;
       
    outFile.open("output1.txt");
    outFile2.open("output2.txt");

        outFile2<<"Chapter 2 Problem 7b Implement the code in the language"<<endl;
                outFile2<<"of your choice, and give the running time for several values of N"<<endl<<endl;
       
int Sum=0;
       
        outFile2<<"For the for loop: for(i = 0; i < n; i++)"<<endl<<endl;

        for (int iterationcountselector = 0; iterationcountselector < vSize; ++iterationcountselector)
        {
                start=clock();
                for(int i =0; i < vec[iterationcountselector] ; i++)
                {
                        Sum++;
                        outFile<< Sum<<endl;
                }
       
                finish=clock();
                duration=(double)(finish-start)/CLOCKS_PER_SEC;
                outFile2<<"Total Time Duration for vector:"<<vec[iterationcountselector]<<" "<< duration<<" ms"<< endl;

        }

outFile2<<endl<<endl;
///////////////////////////////////////////////////////////////////////
outFile2<<"For the loops:for(int i =0; i < vec[iterationcountselector]; i++)"<<endl;
outFile2<<"                  for(int j = 0; j < vec[iterationcountselector]; j++)"<<endl<<endl;
Sum=0;
        for (iterationcountselector = 0; iterationcountselector < vSize; ++iterationcountselector)
        {
               
        start1=clock();
                for(int i =0; i < vec[iterationcountselector]; i++)
               
                {
                        for(int j = 0; j < vec[iterationcountselector]; j++)
                       
                        Sum++;
                        outFile<< Sum<<endl;
                       
                }
       

                finish1=clock();
                duration1=(double)(finish1-start1)/CLOCKS_PER_SEC;
                outFile2<<"Total Time Duration for vector:"<<vec[iterationcountselector]<<" "<<duration1<<" ms"<< endl;
        }
outFile2<<endl<<endl;
//////////////////////////////////////////////////////////////////////
outFile2<<"For the loops:for(int i =0; i < vec[iterationcountselector]; i++)"<<endl;
outFile2<<"                  for(int j = 0; j < vec[iterationcountselector] * vec[iterationcountselector]; j++)"<<endl<<endl;
Sum=0;
for (iterationcountselector = 0; iterationcountselector < vSize; ++iterationcountselector)
        {
               
        start2=clock();
                for(int i =0; i < vec[iterationcountselector]; i++)
                {
                        for(int j = 0; j < vec[iterationcountselector] * vec[iterationcountselector]; j++)
                        Sum++;
                        outFile<< Sum<<endl;
                }
       

                finish2=clock();
                duration2=(double)(finish2-start2)/CLOCKS_PER_SEC;
                outFile2<<"Total Time Duration for vector:"<<vec[iterationcountselector]<<" "<< duration2<<" ms"<< endl;
        }
outFile2<<endl<<endl;
/////////////////////////////////////////////////////////////////////
outFile2<<"For the loops:for(int i =0; i < vec[iterationcountselector]; i++)"<<endl;
outFile2<<"                  for(int j = 0; j < i; j++)"<<endl<<endl;
Sum=0;
for (iterationcountselector = 0; iterationcountselector < vSize; ++iterationcountselector)
        {
               
        start3=clock();
                for(int i =0; i < vec[iterationcountselector]; i++)
                {
                        for(int j = 0; j < i; j++)
                        Sum++;
                        outFile<< Sum<<endl;
                }
       

                finish3=clock();
                duration3=(double)(finish3-start3)/CLOCKS_PER_SEC;
                outFile2<<"Total Time Duration for vector:"<<vec[iterationcountselector]<<" "<< duration3<<" ms"<< endl;
        }
outFile2<<endl<<endl;
////////////////////////////////////////////////////////////////////////
outFile2<<"For the loops:for(int i =0; i < vec[iterationcountselector]; i++)"<<endl;
outFile2<<"                for(int j = 0; j < i; j++)"<<endl;
outFile2<<"                    for(int k = 0; k < j; k++)"<<endl<<endl;
Sum=0;
for (iterationcountselector = 0; iterationcountselector < vSize; ++iterationcountselector)
        {
               
        start4=clock();
                for(int i =0; i < vec[iterationcountselector]; i++)
                {
                        for(int j = 0; j < i; j++)
                                for(int k = 0; k < j; k++)
                        Sum++;
                        outFile<< Sum<<endl;
                }
       

                finish4=clock();
                duration4=(double)(finish4-start4)/CLOCKS_PER_SEC;
                outFile2<<"Total Time Duration for vector:"<<vec[iterationcountselector]<<" "<< duration4<<" ms"<< endl;
}
outFile2<<endl<<endl;
//////////////////////////////////////////////////////////////////////
outFile2<<"For the loops:for(int i =0; i < vec[iterationcountselector]; i++)"<<endl;
outFile2<<"                  for(int j = 1; j < i * i; j++)"<<endl;
outFile2<<"                      if(j % i == 0)"<<endl;
outFile2<<"                          for(int k = 0; k < j; k++)"<<endl<<endl;
Sum=0;
for (iterationcountselector = 0; iterationcountselector < vSize; ++iterationcountselector)
        {
               
        start5=clock();
                for(int i =0; i < vec[iterationcountselector]; i++)
                {
                        for(int j = 1; j < i * i; j++)
                                if(j % i == 0)
                                        for(int k = 0; k < j; k++)
                        Sum++;
                        outFile<< Sum<<endl;
                }
       

                finish5=clock();
                duration5=(double)(finish5-start5)/CLOCKS_PER_SEC;
                outFile2<<"Total Time Duration for vector:"<<vec[iterationcountselector]<<" "<< duration5<<" ms"<< endl;
        }
outFile2<<endl<<endl;

        return 0;
}//end of main

---

Chapter 2 Problem 7b Implement the code in the language
of your choice, and give the running time for several values of N

For the for loop: for(i = 0; i < n; i++)

Total Time Duration for vector:300 0 ms
Total Time Duration for vector:400 0.01 ms
Total Time Duration for vector:500 0.02 ms
Total Time Duration for vector:600 0.01 ms
Total Time Duration for vector:700 0.02 ms
Total Time Duration for vector:800 0.03 ms


For the loops:for(int i =0; i < vec[iterationcountselector]; i++)
for(int j = 0; j < vec[iterationcountselector]; j++)

Total Time Duration for vector:300 0 ms
Total Time Duration for vector:400 0.01 ms
Total Time Duration for vector:500 0.02 ms
Total Time Duration for vector:600 0.02 ms
Total Time Duration for vector:700 0.03 ms
Total Time Duration for vector:800 0.03 ms


For the loops:for(int i =0; i < vec[iterationcountselector]; i++)
for(int j = 0; j < vec[iterationcountselector] * vec[iterationcountselector]; j++)

Total Time Duration for vector:300 0.29 ms
Total Time Duration for vector:400 0.671 ms
Total Time Duration for vector:500 1.302 ms
Total Time Duration for vector:600 2.243 ms
Total Time Duration for vector:700 3.545 ms
Total Time Duration for vector:800 5.268 ms


For the loops:for(int i =0; i < vec[iterationcountselector]; i++)
for(int j = 0; j < i; j++)

Total Time Duration for vector:300 0.01 ms
Total Time Duration for vector:400 0.01 ms
Total Time Duration for vector:500 0.02 ms
Total Time Duration for vector:600 0.02 ms
Total Time Duration for vector:700 0.02 ms
Total Time Duration for vector:800 0.03 ms


For the loops:for(int i =0; i < vec[iterationcountselector]; i++)
for(int j = 0; j < i; j++)
for(int k = 0; k < j; k++)

Total Time Duration for vector:300 0.05 ms
Total Time Duration for vector:400 0.1 ms
Total Time Duration for vector:500 0.201 ms
Total Time Duration for vector:600 0.32 ms
Total Time Duration for vector:700 0.511 ms
Total Time Duration for vector:800 0.741 ms


For the loops:for(int i =0; i < vec[iterationcountselector]; i++)
for(int j = 1; j < i * i; j++)
if(j % i == 0)
for(int k = 0; k < j; k++)

Total Time Duration for vector:300 9.393 ms
Total Time Duration for vector:400 29.423 ms
Total Time Duration for vector:500 71.432 ms
Total Time Duration for vector:600 148.784 ms
Total Time Duration for vector:700 274.505 ms
Total Time Duration for vector:800 473.17 ms