Foundations Updated 2026-09 View as Markdown

Variables and Types

C has several types of variables, but there are a few basic types: The different types of variables define their bounds.

Data types#

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

• Integers - whole numbers which can be either positive or negative. Defined using char, int, short, long or long 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 (long and other numeric data types may have another range on different computers, for example - from –9,223,372,036,854,775,808 to 9,223,372,036,854,775,807 on 64-bit computer).

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

C uses arrays of characters to define strings, and will be explained in the Strings section.

Defining variables#

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.

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 */

The sum of a, b, and c is 12.750000.

#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;
}