C Tutorial – Functions and Global/Local variables
Most languages allow you to create functions of some sort. Functions are used to break up large programs into named sections. You have already been using a function which is the main function. Functions are often used when the same piece of code has to run multiple times.
In this case you can put this piece of code in a function and give that function a name. When the piece of code is required you just have to call the function by its name. (So you only have to type the piece of code once).
In the example below we declare a function with the name MyPrint. The only thing that this function does is to print the sentence: Printing from a function. If we want to use the function we just have to call MyPrint() and the printf statement will be executed. (Don’t forget to put the round brackets behind the function name when you call it or declare it).
Take a look at the example:
#include<stdio.h>
void MyPrint()
{
printf("Printing from a function.\n");
}
int main()
{
MyPrint();
return 0;
}
Parameters and return
Functions can accept parameters and can return a result. (C functions can accept an unlimited number of parameters).
Where the functions are declared in your program does not matter, as long as a functions name is known to the compiler before it is called. In other words: when there are two functions, i.e. functions A and B, and B must call A, than A has to be declared in front of B.
Let’s take a look at an example where a result is returned:
#include<stdio.h>
int Add(int output1,int output2 )
{
printf("%d", output1);
printf("%d", output2);
return output1 + output2;
}
int main()
{
int answer, input1, input2;
scanf("%d", &input1);
scanf("%d", &input2);
answer = Add(input1,input2);
printf(" answer = %d\n", answer);
return 0;
}
The main() function starts with the declaration of three integers. Then the user can input two whole numbers. These numbers are used as input of function Add(). Input1 is stored in output1 and input2 is stored in output2. The function Add() prints the two numbers onto the screen and will return the result of output1 + output2. The return value is stored in the integer answer. The number stored in answer is then printed onto the screen.
Void
If you don’t want to return a result from a function, you can use void return type instead of the int.
So let’s take a look at an example of a function that will not return an integer:
void our_site()
{
printf("www");
printf(".NextDawn");
printf(".nl");
}
Note: As you can see there is not an int before our_site() and there is not a return 0; in the function.
The function can be called by the following statement: our_site();
Global and local variables
A local variable is a variable that is declared inside a function. A global variable is a variable that is declared outside all functions. A local variable can only be used in the function where it is declared. A global variable can be used in all functions.
See the following example:
#include<stdio.h>
// Global variables
int A;
int B;
int Add()
{
return A + B;
}
int main()
{
int answer; // Local variable
A = 5;
B = 7;
answer = Add();
printf("%d\n",answer);
return 0;
}
As you can see two global variables are declared, A and B. These variables can be used in main() and Add().
The local variable answer can only be used in main().
That’s all for this tutorial.
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nice tutorial – thanks.
I think there is a typo in the “Parameters and return” section:
“Input1 is stored in output1 and output2 is stored in Second.”
shouldn’t that be:
“input1 is stored in output1 and input2 is stored in output2.”
Yes, you are right. Changed it. Thx.
There is another typo in the “Parameters and return” code.
anwser = Add(input1,input2);
This should be
answer = Add(input1,input2);
(The spelling of answer is wrong in the 1st statement)
This is an awesome site!!!
@Mujeeb Thx, i’ve changed it!
I think it is best to tell the usage of global variables is not recommended. Especially in a large program.
this is more understandable than the prg. professors of seneca college.
very much useful…, great wrk,,,
clearly understandable….. thanks
great teaching….;)
Thanks, for your great teaching…
nice tutorial thanks
Better And more understandable than profs at BITS.
Thanks .
nice tutorial
useful article ..thanks
Thank you for a great tutorial. My book goes on and on about functions, but never really ties anything together like you did. Examples were used well and explanation was simple and clear. Best ten minutes I ever spent. Thank you!
great
thank you very much….best site
awesome !!!! btr teaching than VIT….. high five !
Its good and easy way to understand tnx
nice , easily understandable
thanks .. this was helpful !!
clearly understandable….. thanks
Thanx for the tutorial.It helped a lot.