C has a concept of 'data types' which are used to define a variable before its use. The definition of a variable will assign storage for the variable and define the type of data that will be held in the location.
The value of a variable can be changed any time.
C has the following basic built-in datatypes.
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int
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float
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double
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char
Please note that there is not a Boolean data type. C does not have the traditional view about logical comparison, but that's another story.
int - data type
int is used to define integer numbers.
| { int Count; Count = 5; } |
float - data type
float is used to define floating point numbers.
| { float Miles; Miles = 5.6; } |
double - data type
double is used to define BIG floating point numbers. It reserves twice the storage for the number. On PCs this is likely to be 8 bytes.
| { double Atoms; Atoms = 2500000; } |
char - data type
char defines characters.
| { char Letter; Letter = 'x'; } |
Modifiers
The data types explained above have the following modifiers.
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short
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long
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signed
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unsigned
The modifiers define the amount of storage allocated to the variable. The amount of storage allocated is not cast in stone. ANSI has the following rules:
| short int <= int <= long int float <= double <= long double |
What this means is that a 'short int' should assign less than or the same amount of storage as an 'int' and the 'int' should be less or the same bytes than a 'long int'. What this means in the real world is:
| Type | Bytes | Range | |
| short int | 2 | -32,768 -> +32,767 | (32kb) |
| unsigned short int | 2 | 0 -> +65,535 | (64Kb) |
| unsigned int | 4 | 0 -> +4,294,967,295 | ( 4Gb) |
| int | 4 | -2,147,483,648 -> +2,147,483,647 | ( 2Gb) |
| long int | 4 | -2,147,483,648 -> +2,147,483,647 | ( 2Gb) |
| signed char | 1 | -128 -> +127 | |
| unsigned char | 1 | 0 -> +255 | |
| float | 4 | ||
| double | 8 | ||
| long double | 12 |
These figures only apply to today's generation of PCs. Mainframes and midrange machines could use different figures, but would still comply with the rule above.
You can find out how much storage is allocated to a data type by using the sizeof operator discussed in Operator Types Session.
Here is an example to check size of memory taken by various datatypes.
| int main() { printf("sizeof(char) == %d\n", sizeof(char)); printf("sizeof(short) == %d\n", sizeof(short)); printf("sizeof(int) == %d\n", sizeof(int)); printf("sizeof(long) == %d\n", sizeof(long)); printf("sizeof(float) == %d\n", sizeof(float)); printf("sizeof(double) == %d\n", sizeof(double)); printf("sizeof(long double) == %d\n", sizeof(long double)); printf("sizeof(long long) == %d\n", sizeof(long long)); return 0; } |
