Programming and Data Types in C programming

In C programming we have different kinds of data types in C language and this is in continuation with previous discussion.

Integers signed and unsigned:

Sample code for syntax for unsigned inter is :

nsigned int num_students ;

With this declaration, the range of permissible integer values (for a 16-bit OS) will shift from the range -32768 to +32767 to the range 0 to 65535. Thus, declaring an integer as unsigned almost doubles the size of the largest possible value that it can otherwise take.

It happens because on declaring the integer as unsigned, the left-most bit is now free and is not used to store the sign of the number.

Unsigned integer still occupies two bytes.

It can be declared as : unsigned int i ; unsigned i ;

There also exists a short unsigned int and a long unsigned int. By default a short int is a signed short int and a long int is a signed long int in C programming.

Chars, signed and unsigned

Signed and unsigned chars, both occupying one byte each, but having different ranges. Consider the statement

char ch = 'A' ;

Here what gets stored in ch is the binary equivalent of the ASCII value of ‘A’ (i.e. binary of 65). And if 65’s binary can be stored, then -54’s binary can also be stored (in a signed char).

A signed char is same as an ordinary char and has a range from -128 to +127; whereas, an unsigned char has a range from 0 to 255.

Floats and Doubles

A float occupies four bytes in memory and can range from -3.4e38 to +3.4e38. If this is insufficient then C offers a double data type that occupies 8 bytes in memory and has a range from -1.7e308 to +1.7e308.

A variable of type double can be declared as,

double a, population ;

If the situation demands usage of real numbers that lie even beyond the range offered by double data type, then there exists a long double that can range from -1.7e4932 to +1.7e4932.

A long double occupies 10 bytes in memory in c programming and it is used rarely.

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Programming and Data Types

Primary data types of programming could be of three varieties—char, int, and float. We can derive many data types from these three types.

A char could be an unsigned char or a signed char. Or an int could be a short int or a long int.

Integers, long and short We had seen earlier that the range of an Integer constant depends upon the compiler.

For a 16-bit compiler like Turbo C or Turbo C++ the range is –32768 to 32767.
For a 32-bit compiler the range would be –2147483648 to +2147483647.

16-bit compiler means that when it compiles a C program it generates machine language code that is targeted towards working on a 16-bit microprocessor like Intel 8086/8088.

A 32-bit compiler like VC++ generates machine language code that is targeted towards a 32-bit microprocessor like Intel Pentium.
A program compiled using Turbo C would not work on 32-bit processor. It would run successfully but at that time the 32-bit processor would work as if it were a 16-bit processor.

This happens because a 32-bit processor provides support for programs compiled using 16-bit compilers. If this backward compatibility support is not provided the 16-bit program would not run on it.

Out of the two or four bytes used to store an integer, the highest bit (16th/32nd bit) is used to store the sign of the integer. This bit is 1 if the number is negative, and 0 if the number is positive.

C offers a variation of the integer data type that provides what are called short and long integer values.

Short and long integers would usually occupy two and four bytes respectively. Each compiler can decide appropriate sizes depending on the operating system and hardware for which it is being written, subject to the following rules:

• shorts are at least 2 bytes big
• longs are at least 4 bytes big
• shorts are never bigger than ints
• ints are never bigger than longs

long variables which hold long integers are declared using the keyword long.

Long integers cause the program to run a bit slower, but the range of values that we can use is expanded tremendously. The value of a long integer typically can vary from -2147483648 to +2147483647.

Integers that need less space in memory and thus help speed up program execution.

Short integer variables are declared as,

short int j ;
short int height ;

C allows the abbreviation of short int to short and of long int to long. So the declarations made above can be written as,

long i ;
long abc ;
short j ;
short height ;

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INTRODUCTION TO C PROGRAMMING

Programming with C an introduction part two

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