The header file for advanced mathematical functions is math.h, surprise
Making a word a variable requires the use of an array, referred to as a string in this case. There's not a string data type, so you have to use a char array.
result = sqrt(num);
The first scanf will allow you to enter a single word, but as soon as it reads in a space it will stop. The second scanf will read until it sees a newline, meaning it will read into the array until it reaches the point where you hit enter.
printf("Enter your first name: ");
printf("Your first name is %s\nEnter your whole name: ", array1);
printf("Your whole name is %s", array2);