Tuesday, 12 June 2012

List of keywords in C with Descriptions

Keywords in C 

 


auto
    "auto" Keyword is used to define a variable of storage class automatic. 
For example:

    auto int var1;

    This statement is suggest that var1 is a variable of storage class auto and data type int.
Variables declared within function bodies are automatic by default.  They are recreated each time a function is executed. Since, automatic variables are local to a function, automatic variables are also called local variables.


break and continue
    The break statement is used to jump out of the innermost enclosing loop (while, do, for or switch statements) explicitly and pass control to next statement immediately following the loop. In other hand, continue statement is used to skip certain statements inside the loop.

    for(i=1;i<=10;++1){
    if(i==3)
    continue;
    if(i==7)
    break;
    printf("%d ",i);
    }

    The output of the given code is: 1 2 4 5 6. It is because, when i=3, continue statement comes to effect and skips 3 and when i=7, break statements come to effect and terminates the loop.
switch, case and default
    The "switch" statement tests the value of a expression and test with the different "case" values. We can use "default" value, if it doesn't matches any of "case" values. For example:

    switch(option){
    case '1':
    //some statements to execute when 1
    break;
    case '5':
    //some statements to execute when 5
    break;
    default:
    //some statements to execute when default;
    }

char
    The char keyword is used to indicated the variable is of the type character.For example:

    char variable0;

    Here variable0 is a variable of type character 
const
    "const" keywords makes the value of a pointer or a variable modifiable.

    const int a=5;

    In this example, a is the constant and its value is 5. This value cannot be changed in program.
do and while
    "while" and "do" keywords are used during looping in C.For example:

    i=2;
    while (i<10){
    print("%d ",i)
    i++;
    }

    Output: 2 3 4 5 6 7 8 9. If programmer finds easy to write condition of loop after the statements that are executed by while loop, do...while statement is used using "do" keyword.

    int 2;
    do{
    print("%d ",i)
    i++;
    }
    while (i<10)

    The output of this example is same as before, only the way of writing program is changed.

double and float
    "double" and"float" keywords are used to indicate floating type variables. Keywords float and double represents single precision and double precision floating point data respectively. For example:

    float variable1;
    double variable2;

    Here, variable1 is single precision floating type variable whereas, variable2 is double precision single precision gloating type variable.

if and else
    Keywords "if" and "else" are used in decision making in C.

    if(i==1)
    printf("i is 1.")
    else
    prinf("i is not 1.")

    Output will be "i is 1." if i=1. If value of i is other than 1, output will be "i is not 1."

enum
    Keyword "enum" is used to define enumerated by data type. Enumerated data type creates a set of constant of type int.For example:

    enum enum_var{
    var_1;
    var_2;
    var_3;
    };

    Here, a enumerated variable enum_var is created having tags: var_1, var_2 and var_3.

extern
    Keyword "extern" is used to indicated the variable is external and is declared outside every function and can be accessed by any function. For example:

    #include <stdio.h>
    extern i=5;
    void print1() {
    printf ("%d ",i);
    }
    int main() {
    printf("%d ",i);
    }
    return 0;
    }

    Output: 5 5


for
    Keyword "for" is used for looping in C. For example:

    for(i=0;i<9;++i){
    printf("%d ",i);
    }

    Output: 0 1 2 3 4 5 6 7 8

goto
    Keyword "goto" is used for unconditional jump to a labeled statement inside that function. For example:

    for(i=1;i<15;++i){
    if(i==10)
    goto error;
    }
    printf("i is not 10");
    error:
    printf("Error, count can't be 10");

    Output: Error, count can't be 10. It because, when i equals to 10,control of program jumps to label.i.e. error: in this case.

int
    Keyword "int" is used to indicated the variable is of type integer.

    int var0;

    Here, var0 is a variable of type integer.

short, long, signed and unsigned
    Keywords "short","long", "signed" and "unsigned" are type modifiers that alters the meaning of base data type to yield new type

    short int var1;
    long int var2;
    signed int var3;
    unsigned int var4;

    Here, the int types variable are modified to short int, long int, signed int and unsigned int respectively.
    Range of int type data types
    Datatypes     Range
short int     -32768 to 32767
long int     -2147483648 to 214743648
signed int     -32768 to 32767
unsigned int     0 to 65535

return
    Keyword "return" terminates the execution of current function and returns the value to the calling function.

    int func(){
    int b=5;
    return b;
    }

    This function func() returns 5 to to the calling function.

sizeof
    Keyword "sizeof" is used to find the number of bytes of an object.

    #include <stdio.h>
    int main(){
    printf("%u bytes.",sizeof(char));
    }

    Output: 1 bytes. Here, sizeof(...) is used to find the number of bytes of type char.

register
    Keyword "register" is used to indicate the register of storage class register. Variable of storage class register are much faster than normal variables.

    register int var1;

    Here, var1 is the variable of storage class register.

static
    Keyword "static" is used to indicate the variable is of storage class static. The value of the static variables persists until the end of the program. For example:

    static int var;

    Here, var is a variable of storage class static.

struct
    Keyword "struct" is used in creating a structure which provide means to group different types of variable under one name for easier handling.

    struct student{
    char name[80];
    float marks;
    int age;
    }s1,s2;

    Here, struct keyword is used in creating a structure of tag name student and variables of type struct student.

typedef
    Keyword "typedef" is used to explicitly associate a type with an identifier.

    typedef float kg;
    kg bear,tiger;

    Here, the use of typedef is to create a type kg and this kg type is used in declaring variables bear and tiger.

union
    Keyword "union" is used in creating a union which provide means to group different types of variable under one name for easier handling.

    union student{
    char name[80];
    float marks;
    int age;
    }

    Here, union keyword is used in creating a union of tag name student and variables of type union student.

void
    Keyword "void" is used to indicate that a function takes no arguments or returns no value.

    void no_return(int a){
    .....
    }

    Here, function no_return can take value but, can't return value because, the return type is void.

volatile
    Keyword "volatile" is used to create a volatile object. A volatile object can be modified in unspecified way by the hardware.

    const volatile number

    Here, number is a volatile object. Since, number is constant variable, program can't change it but, hardware can change it because, it is a volatile object.

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This post was written by: Suresh kumar


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