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User Defined Functions in C

Almost all the programming languages uses functions. Functions are the entities which are grouping a set of statements which do a specific job or set of jobs.
Example: sum of integers, sum of float number, complex number addition.
All the above three can be implemented as a single function or three separate functions.
When someone wants to use that, a function can be simply called.
So function implementation happens as
  • Function prototype or Function declaration
  • Function definition or function implementation
  • Function call
Function prototype
  • It is necessary to specify the name of the function, the parameters and the return type to the compiler that the function is being defined in this program.
  • The prototype ends with a semicolon
int sum(int, int); //function prototype
Function Definition
This is the actual function definition which shows the function implementation.
for the above syntax here is the function
int sum(int a, int b)
int c;
return c;
The above function is returning an integer, hence int is specified. If a function is not returning any thing, a void can be used.
Function call
The last is the function call, which when being needed a simple call will make the function to work. Here is the example
int main()
int x,y,z;
scanf(“%d %d”,&x,&y);
z=sum(x,y); //function call
printf(“The sum is %d”, z);
return 0;
Once the function is called, the control goes to the actual implementation and execute the statements inside the function and the value is returned to the main function.
Components of a function
  1. Name of the function
  2. Return type
  3. Parameters or arguments
In the above example
name of the function is : sum()
return type is : int
parameters are: int, int

 T S Pradeep Kumar


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