How on earth to use char and if statements?

I'm a rookie programmer trying to run a simple code on VS code.

#include<stdio.h>

int main()
{
char* a;

printf("Enter a char");
scanf("%s",&a);

if (a = "yes")
{
    printf("Number is 30");
}
else if (a = "no")
{
    printf("Number is 50");
}
else{
    printf("oops");
}

return 0;
}

I guess looking at the code you guys can figure out what I'm trying to do, if the user enters "yes", a specific sentence need to be displayed and similarly for "no". The problem here is whatever I write in the input, it will always print the first statement, "Number is 30". I've tried running similar codes but ended up with the same output.

If possible, please explain me how to use char,strings,arrays with if-else statements.