int var; char var; short var; long var; etc.
To define a variable you have to write a datatype first. After then, you write the name of the variable. It mustn't begin with a number and it mustn't contain a special character except "_". You can also give it immediately a value; that's called initializing.
#include <stdio.h>
int main()
{
	int var1;//an integer
	var1=5;//gives a value
	char var2=65;//give a value immediately after defining -> initializing
	printf("Var1: %d \n",var1);
	printf("Var2: Character: %c number: %d \n",var2,var2);
	return 0;
}
/*
	well, here are much samples for variable types:

	name            poss. value

	char            -128 -> 127
	unsigned char   0 -> 255
	short           -32768 -> 32767
	unsigned short  0 -> 65535
	int             -2147483648 -> 2147483647
	unsigned int    0 -> 4294967295
	long            the same as int
	unsigned long   the same as unsigned int
	float           -/+3.4*10^-38 -> -/+3.4*10^38
	double          -/+1.7*10^-308 -> -/+1.7*10^308
	long double     -/+3.4*10^-4932 -> -/+3.4*10^4932
	
	there are also definitions for print with printf()
	specification   meaning

	%c              char,int; a symbol from ASCII(0-255)
	%d              decimal output()
	%ld             long; the same as %d, but with long  
	%u              unsigned int; decimal output
	%lu             unsigned long; the same as %u, but with unsigned long
	%o              oktal output
	%x              hexadecimal output

*/