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


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