Variables and Types

Data types

C has several types of variables, but there are a few basic types:

• Integers - whole numbers which can be both positive and negative. Defined using char, int, short, long orlong long.
• Unsigned integers - whole numbers which can only be positive. Defined using unsigned char, unsigned int,unsigned short, unsigned long or unsigned long long.
• Floating point numbers - real numbers (numbers with fractions). Defined using float and double.
• Structures - will be explained later, in the Structures section.

The different types of variables define their bounds. A char can range only from -128 to 127, whereas a long can range from -2,147,483,648 to 2,147,483,647.

Note that C does not have a boolean type. Usually, it is defined using the following notation:

#define BOOL char
#define FALSE 0
#define TRUE 1

For numbers, we will usually use the type int, which an integer in the size of a "word" the default number size of the machine which your program is compiled on. On most computers today, it is a 32-bit number, which means the number can range from -2,147,483,648 to 2,147,483,647 (same as long).

To define the variables foo and bar, we need to use the following syntax:

int foo;
int bar = 1;

The variable foo can be used, but since we did not initialize it, we don't know what's in it. The variable bar contains the number 1.

Now, we can do some math. Assuming a, b, c, d, and e are variables, we can simply use plus, minus and multiplication operators in the following notation, and assign a new value to a:

int a = 0,b = 1,c = 2,d = 3, e = 4;
a = b - c + d * e;
printf("%d", a); /* will print 1-2+3*4 = 11 */

#include <stdio.h>

int main() {

  int a = 3;

  float b = 4.5;

  double c = 5.25;

  float sum;

  sum = a + b + c;

  printf("The sum of a, b, and c is %f.", sum);

  return 0;

}
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