Data structure scope of variables

Data structure scope of variables

• 1.
  Data Structure Scope of Variables Prepared By.. Kumar Saurav Kumar Shaambhavi Pathak CS- B. tech CS-Oil &Gas Info CS- B. tech CS-Oil &Gas Info 500016630 500016891 R970211046 R970211047 2011- 2011-2015 2011- 2011-2015
• 2.
  In very simplewords, scope of a variable can be defined as a validity of a variable or other identifier within which its declaration has an effect. A C program consists of multiple functions classes code structures (like while, for, do-while loops).A Normal program makes use of variables or other identifier under any functions for manipulation or storage purposes. Now, once the code is written it may or may not be accessible for the other section of the code. This accessibility depends upon the declaration of the variables that how it was declared and where it was declared. This comes under variable scope scope. There are different types of variable scope. •Block Scope Block •Function Scope Function •Global Scope •File Scope Now, let us Get down To each of them One by One.
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  Block Scope C programis divided into many blocks of codes. They are mostly embraced ({}).For example, for loop has a statement block. It is Also Said to have a local scope. Look these codes: #include<stdio.h> //header file main() { int i; //local variable for(i=0;i<5;i++) { int j=i*i; printf(“nValue of j is %d”,j); } //printf(“nValue of j is %d”,j); }
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  As seen fromthe output screen that if the comment statement is not executed the program runs well in code blocks IDE. Now,The Difference lies here… #include<stdio.h> main() { int i; for(i=0;i<5;i++) { int j=i*i; printf(“nValue of j is %d”,j); } printf(“nValue of j is %d”,j); }
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  Follows by anerror..!! The explanation behind this is that the variable j is only valid inside the for loop but not outside. This Concludes the Block Scope. Function Scope C program typically are structured with classes and codes called function. Each function is capable of performing its own prescribed task and takes in arguments and return a values and further depends on which type is it. Concept to know: Variable declared within a function is accessible only under that function and those variables are called local variables. Look to this piece of code: #include<stdio.h> int fact(void); //function declaration
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  main() { int n,res; printf(“nEnter a no “); scanf(“%d”,&n); res=fact(n); printf(“nValue is %d”,res); } int fact (void) { int res; //local variable in fact function if(n!=1) { res=n*fact(n-1); return(res); } else { return(1); } }
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  Any Guess Whatthe error would be..?? Its due to that we are neglecting the the function scope. Lets try Improving our code.. #include<stdio.h> int fact(int); main() { int n,res; printf(“nEnter a no “); scanf(“%d”,&n); res=fact(n); //function call printf(“nValue is %d”,res); } int fact (int n) { int res; if(n!=1) { res=n*fact(n-1);
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  return(res); } else { return(1); }} Now when we Corrected/declared local variable in fact function the program runs well…!! Thus we see that here in the function scope the local variable once declared in one function is not accessible in any other function. This concludes the basic of Function scope. Global Scope A global scoped variable can be accessed through any Where in the code irrespective of the function or file. It is usually placed just below the source file. It is also said to have a Program Scope.
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  Let us examinethis code: #include<stdio.h> int array[5]; //global array declaration void next(void); //function declaration main() { int a; for(a=0;a<=2;a++) { array[a]=a+1; //inserting values in globally created array } next(); //function call printf(“n”); for(a=0;a<5;a++) //loop for printing the stroed values in the array { printf(“t%d”,array[a]); } } void next(void) { int b; for(b=3;b<=4;b++) { array[b]=b+1; }
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  } Hence From theabove output it clearly shows that the global variable can be accessed throught any piece of code. However, if a variable name is declared same in two different scopes(i.e global and block),then any change made inside the block code for that variable will change the value of the variable for that variable inside the block. Same if any change is made outside the global variable’s value will be altered..!! Let us Examine this concept through the following code: #include<stdio.h> int out=50; //global variable main() { { int out=50; //local variable out=out+50; printf("nTha value of variable out inside the block is %d",out); } printf("nThe value of out variable outside the block is %d",out); }
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  The 1st outputis 100 while the second output is 50.This example shows that block scope is valid inside block (Note SAME NAME OF GLOBAL VARIABLE IS THERE Note: THERE). This Basically concludes the Global variables. Now, before we begin with our next variable scope (file scope) we must learn about variable storage classes classes. Sometimes we need to mention or declare the variables according to our programming needs. Variable storage class specifiers are used when declaring a variable to give the compiler information about how a variable is likely to be used and accessed within the program being compiled. •Static •Extern •auto •const
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  •volatile Here we shalldiscuss only about static. Static as a Variable storage Class It specifies that a variable is to be accessible only within the scope of current source file when it is declared globally. when it is declared under any function then it its value don’t die even after the execution. This was just to introduce Static as a variable storage class. Now when static is either used with global variables or local variables. Let us see an example of static used with Global variable. #include<stdio.h> static int marks=100; //static global variable main() { //statements } Initially global variables could be used anywhere in the programme or even in another file.
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  When we usestatic, this variable aquires file scope meaning that this variable is valid only in the current file and not in any other file. Now let us see an example of static used with local variable.. #include<stdio.h> void fun(); main() { int i; for(i=0;i<5;i++) { fun(); } } void fun() { static m=0; m++; printf("t%d",m); } If you got output as 1 1 1 1 1 Then, you need to look at your work again..!!
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  Due to thestorage class static the value of m remains conserved..!! So here is the output : This concludes the lesson. Sources: http://www.learncpp.com/cpp-tutorial/43-file-scope-and-the-static-keyword/ http://www.techotopia.com/index.php/Objective-C_Variable_Scope_and_Storage_Class http://icecube.wisc.edu/~dglo/c_class/scope.html