The declaration and the usage of the variable in the foregoing paragraph though it explained
It hardly explained the type when declaring a variable.

To declare a variable in the foregoing paragraph, it explained the following writing was used.

Type name variable identifier;

In C language, a variety of kinds of numerical values can be treated.
And, it is necessary to memorize it by using a separate kind of variable of the each numerical value.
A variety of kinds of numerical values might be called a data type in this manner.

[   Data type   ]
Kind of of numerical valueThe size and the form of presentation are different.

There are not too a lot of kinds of the data type used by C language.
There is no problem as long as the following two between now are remembered.

Type name	Kind of numerical value
int	Integer
double	Real number

The variable that had been used ahead was int type.
The kind of variable of another one and double (double) types can be used besides it.
The double type is a type that memorizes the real number while the int type memorizes the integer.

The usage is quite the same. only different the kind of the memorized numerical value this two
The following program is an example of doing the arithmetic operation by using the double type.

 
#include <stdio.h> 

int main(void)  
{
	double left,right;  
	left = 10;  
	right = 3;  
	printf("%f\n",left + right);  
	printf("%f\n",left - right);  
	printf("%f\n",left * right);  
	printf("%f\n",left / right);  
	return 0;
}

13.000000
7.000000
30.000000
3.333333