Characters and Strings
In assembly language, character data is represented using ASCII (American Standard Code for Information Interchange) values, and specific instructions handle the manipulation and storage of these characters in memory.
Characters are represented by ASCII values, which are numerical codes assigned to each character. For example, the ASCII value for 'A' is 65.
Registers and Memory
Character data is stored in registers or memory locations, and assembly instructions like MOV are used to transfer data between them.
Strings, which are sequences of characters, are manipulated using string-specific instructions. These include loading, storing, and comparing strings.
Assembly language supports instructions for character input and output. For example, DOS interrupts can be used for displaying characters on the screen.
Comparison and Branching
Character data can be compared using instructions like CMP (compare) and conditional branches (e.g., JE for jump if equal).
Assembly language programmers can also use character data to implement more complex functions, such as string manipulation functions and text editors.
Here is an example of a simple assembly language function that copies a string from one memory location to another.
Above code defines a function named copy_string that copies a null-terminated string from a source memory location (src) to a destination memory location (dst). The function uses the AL register to temporarily store the current byte from the source and then stores it into the destination. It increments both the source and destination pointers, checks if the end of the string has been reached by comparing the byte at the source with 0 (null terminator), and repeats the process until the end of the string is encountered. The main section (_start) initializes source and destination strings, calls the copy_string function, and exits the program with a syscall. Note that the code assumes a 32-bit architecture and uses the x86 instruction set.
Character data is represented using ASCII values and manipulated through instructions like MOV for storage in registers or memory. Specific operations, such as string manipulation and character input/output, are facilitated by assembly language instructions tailored for handling character-based information.