I was making a code that adds a summation for a specific formula, but the sum is always 0 for some reason. What is the reason nothing is adding? I think maybe it is the declaration of int and double for the variables. When I do a simple equation, such as adding natural numbers, it works, but not for more complicated equations like the one below.

Code:

#include <stdio.h>

int main()
{
    int i, n;
    double sum = 0;
    printf("Enter the max value for the sum: ");
    scanf("%d", &n);
    i = 1;

    while(i <= n)
    {
        sum = sum   (1 / ((1   i) * (1   i)));
        i  ;
    }
    printf("Sum = %f\n", sum);  
}

I tried the code pasted above, expected the correct sum, but resulted in only 0.0000.

CodePudding user response：

In this statement

sum = sum   (1 / ((1   i) * (1   i)));

the sub-expression (1 / ((1 i) * (1 i))) uses the integer arithmetic. It means that if to divide 1 by any integer number greater than 1 the result will be equal to 0.

'You need to use the arithmetic with float numbers.

It will be enough to write

sum  = 1.0 / ((1   i) * (1   i));

Or it will be even more better to write using long long int constant 1ll like

sum  = 1.0 / ((1ll   i) * (1   i));

to avoid overflow for the integer multiplication.

Also as the range is specified as two positive numbers then it will be logically better to specify the variables i and n as having the type unsigned int.

CodePudding user response：

Check how division of ints is defined.

CodePudding user response：

You need to cast the result of the divison as a double since that is what you are expecting as a result. Int division will round it to closest whole number