int 1a, b;
int 1a, b; $\Rightarrow$ error: invalid suffix "a" on integer constant
This gives a $lexical\space error$. This is because in C, the first character of a variable name should be either a letter or an underscore.
Printf("\nGate 2018"); $\Rightarrow$ warning: implicit declaration of function 'Printf'
$Semantic\space error$ at Printf. C is a case sensitive language and function used to print is printf. The program identifies 'Printf' as a new function and gives 'function not declared' error.
Printf("%d",x); $\Rightarrow$ error: 'x' undeclared (first use in this function)
This is a $semantic\space error$ again, as x is used here before declaring.
So, the $number\space of\space types$ of errors in this code is $2$. (Lexical error and Semantic error)