User define function in C programming

What is a function in C programming?

User-defined function in C programming

The function is like some tasks defined in a group of instructions. If we call the function, it's do something for us and sometimes return something.
For example, let's think about a factory that inputs some Raw material and processes it, then gives us some output. Like a blending machine. We input water, ice, sugar, lemon, and the output is lemon juice.
In a function, there is some instruction and when we call it, it gives us some results according to the instruction.

Every c program must have at least one function called the main function looks like main(). There are many library functions in C, like as printf ( ); scanf( ); etc. Again we can write functions our-self.

Basic structure of a function:

return_type function_name( parameter list ) { body of the function }

* Return type: Return type is the kind of output of the function. For the blending machine, the output is "lemon juice". So here return type is liquid.
* Function name: It's just the name of the function. Like "blending machine".
* Parameter list: The parameter list is the input list. Here water, ice, sugar, lemon.
* Body of the function: The instruction of processing our inputs. 

Example: 

#include <stdio.h> #include <stdlib.h> int add(int a, int b) // User define function which return sum of two number. { int c; c = a+b; // processing method or instruction return c; } int main() { int c = add(2,2); // Calling function and passing argument or input printf("Result is %d!\n", c); return 0; }

Output:
Result is 4!

Explanation:

In basic instruction:

return_type function_name parameter list

is define as:

int add(int a, int b)

Here returns type is an integer. The parameter type is important. Here are two parameters a and b which are integer types. So, we have to pass the integer type argument as input.

int c = add(2,2);

Benefits of function:

If we need to do the same processing in many places of our code, we have to write the same code again and again. Like as if we need to add two numbers several times, we can write a function and call it again and again.

Like as:

int main() { int c = add(2,2); // Calling function and passing argument or input (First time) int d = add(4,6); // Second time int e = add(10,50);// Third time[We can call add function unlimited times] printf("1st Result is %d!\n", c); printf("2nd Result is %d!\n", d); printf("3rd Result is %d!\n", e); return 0; }

Output:
1st Result is 4! 2nd Result is 10! 3rd Result is 60!

Another Example:

#include <stdio.h> #include <stdlib.h> void print_msg()/*Return type void, that's means it will not return anything*/ { printf("Hello !!!\n"); } void added_all(long int val)/*Return type void, that's means it will not return anything*/ { int n; long int sum; sum=0; for(n = 0;n<=val; n++) sum+=n; printf("Sum of all number from 1 to %d is: %d",val,sum); } int main() { print_msg(); added_all(500);//passing argument to function return 0; }

Output:
Hello !!! Sum of all number from 1 to %d is: 125250

I hope it helps to understand function declaration and how to use the function, make function.
Happy coding!!!

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