c++ - i want to calculate the T(n) for the two algorithms -

i want know time complexity following 2 algorithms

void main (){-----------------------------------------t(n) for(int a=1 ; a<=20 ; a++) {------------? if(a%2==0)  -------------?     cout<<"value even"; --------?    else       cout<<"value odd";--------? } 

}

void main (){-----------------------------------------t(n) int x=1; {------------? int a=1;  -------------?    while(a<=n){--------?    x=x*a; -------------?    a=a+2; -------------?   } cout<<x; } 

the idea calculate how execution time piece of code - typically algorithm, depends on input. if function takes n input how long take execute if n=5 or n=10. take double long? take same time? or take more double?

in case:

the first program doesn't depend on input o(n)=1.

your second program depends on n. same stuff n/2 times due = + 2. o(n)=n/2. constants typically skipped , 1 write o(n) = n.

if had code this:

for (a=0; < n; a++) {      // n times here      (b=0; b<n; b++)      {         // n times here          //      }  } 

the execution time change n^2 because both loops iterate n times. each time outer loop executes, inner loop executes n times. since outer loop executes n times, have n*n. o(n) = n^2