Strange behaviour of the pow function

Question

While running the following lines of code:

int i,a;    

for(i=0;i<=4;i++)  
{    
    a=pow(10,i);    
    printf(\"%d\\t\",a);    
}   

Answer 1

Mathematically, the integer power of an integer is an integer.

In a good quality pow() routine this specific calculation should NOT produce any round-off errors. I ran your code on Eclipse/Microsoft C and got the following output:

1   10  100 1000    10000   

This test does NOT indicate if Microsoft is using floats and rounding or if they are detecting the type of your numbers and choosing the appropriate method.

So, I ran the following code:

#include 
#include 
main ()
{
    double i,a;

    for(i=0.0; i <= 4.0 ;i++)
    {
        a=pow(10,i);
        printf("%lf\t",a);
    }
}

And got the following output:

1.000000    10.000000   100.000000  1000.000000 10000.000000