Percentage Calculation in Solidity

Question

I am wondering if my idea is correct.

Total shares: 11,000

User A's shares : 10,000

User A's share percentage = User A's share / Total share.

                      = 10,000 / 11,000
                      = 0.90909090909 
                      = 0 in solidity

However, Solidity does not support float, so I rewrite

User A's share percentage = User A's shares * 10,000 / Total shares.

                      = (10,000 * 10,000) / 11,000
                      = 9090.9090909
                      = 9090 in solidity  

User A's shares = total shares * User A's share percentage / 10,000

                      = (11,000 * 9,090 ) / 10,000
                      = 9999

User A's shares is 9999, but it should be 10,000. How do I correct my math?

Answer 1

One way to achieve this is by utilizing a decimals variable, which defines the maximum number of decimal places the contract can support.

In your case, use a new decimals constant.

decimals = 2;

User A's share percentage = User A's shares * 10,000 / Total shares.

              = (10,000 * 10,000) / 11000) * (10^2)
              = 909090.90909
              = 909090 in solidity  

User A's shares = total shares * User A's share percentage / 10,000

              = (11,000 * 909090 ) / 10000
              = 999999    

Outside solidity, you can do the rounding process
       result = 999999 / decimals
// other languages which support flow has a higher accuracy for rounding
       result = 9999.99  
       result = 10000
   

By specifying an appropriate range for the decimals variable, you can ensure that the rounding process aligns with your specific requirements for accuracy.