Local and Global variables
There are two types of variables: local and global variables
Local variables:
Local variables are defined within the body of the function or the block({}). The variable defined is local to that function or block only. Other functions cannot access these variables. The compiler shows errors in case other functions try to access the variables.
In above figure, value1, value2, value3 and value5 are local variables. These are also called automatic variables.
Global Variables:
Global variables are defined outside the main() function.
Multiple functions can use them. The example is illustrated below for understanding.
The variable value1, which appears at the beginning of the file, is declared at global scope, as is ‘value4’, which appears after the function main(). The scope of each global variable extends from the point at which it is defined to the end of the file. Even though value4 exists when execution starts, it cannot be referred to in main(), because main() is not within the variables scope, which is not the case for the automatic variables.
Usage of global variables is not encouraged.
Function Prototypes
In ‘C’, we use many built-in functions. the prototypes of these functions are given in the respective header files. Also, while defining user-defined functions, we must declare its prototype. A prototype statement helps the compiler to check the return type and argument type of the function.
A function prototype declaration consists of the functions return type, name and arguments list. When the programmer defines the function, the definition of the function must be the same like its prototype declaration. If the programmer makes any mistake, the compiler flags an error message. The function prototype declaration statement is always terminated with a semi-colon. The statements given below are examples of function prototypes.
Syntax of the function prototype
return_type function_name (type arg1, type arg2, ...... type arg n);
Example:
float sum(float x,inty);
/* In the above example the prototype functions sum() is declared. Its return value is float and arguments are float and integer type respectively */
