Introduction to C language

Introduction to C

     C is a general purpose programming language. Programming language is the means to communicate with the system to get our thing done.

Need for a programming language:

  We all of us know system can only understand binary representation i.e. in the form of 0's and 1's.

Suppose we have to program which adds two numbers and save the result.

Steps involved:

• First we should write the values in the memory.
• Move those values into the registers.(registers are also a kind of memory where the CPU can perform operation on the values stored in the registers.)
• Add the values in the registers.
• Save the result in the register to the memory.

Machine Language                                                                                                                                                                                                                                                                               At the beginning machine code is used to write the program. 

Machine level programming consists of binary or hexadecimal instructions on which an processor can respond directly.  

Structure of machine language instruction.

Opcode   Operand 

Opcode represents the operation to be performed by the system on the operands.

In machine code:

Memory     opcode     operand 

location                                                                     

0000:           55            e4     10   // 55 represent move instruction, move 10 to location e4          

0001:           89            e5     20

0003:           83            e4     e5

0006:           54            c4     e4    

Its difficult to read and write opcode for every instruction. So instead of numerical value for instruction there should be an alternative, Then comes the assembly code.

Assembly language:

 Mnemonics are used to represent the opcode.

An Assembly code:

MOV  A, $20           // move value 20 to register A (MOV is a mnemonics)

MOV  B, $10           // move value 10 to register B

ADD   A, B              // Add value in register in A and B

MOV  #30, A           // move value in register A to address 30

Assemblers converts the assembly language into binary instructions.

Assembly language is referred to as low level language,

Assembler languages are simpler than opcodes. Their syntax is easier to read than machine language but as the harder to remember. So, their is a need for other language which is much more easy to read and write the code.

Then comes the C programming language.

C language

In C language:

 int main()

{

     int a,b,c;

     a=10;

     b=20;

     c=a+b;

}

Compiler converts the C language code into assembly language code.

C language is easier to write and read.