calculation of [H+]

I know that
pH= -log[H+]

But it can be used when i know the pH value of the solution
Can we calculate the concentration of hydrogen ion when we know the volume of the solution and the mass of solute?
For example
In 200cm3 HCL, there is 5G HCl , can we calculate the [H+]?

Is it like:
num of mol of hcl:5/(1+35.5)=0.137mol
num of mol of h+:0.137 mol

molarity:0.137/0.2=0.685M

[h+]= 0.685??????


it is correct?
if yes, [h+]= molarity?
if no, please show me how to calculate~~
Thanks for help!!!