The versatility of the computer lies in its adeptness to accomplish a set of instructions repeatedly. This involves repeating some allocation of the affairs either a defined amount of times or until a specific action is getting satisfied.
Various loops availble in C are as follows:

• a for statement 
• a while statement 
• a do-while statement

The codicillary or conditional operators ? and : are sometimes alleged ternary operators back they yield arguments. In fact, they anatomy a affectionate of foreshortened if-then-else. Their accepted anatomy is :


expression 1 ? expression 2 : expression 3


If announcement one is accurate (that is, if its amount is non-zero), again the account alternate will be announcement two, contrarily the account alternate will be announcement 3. Example showing conditional operator:


main( )
{
int a = -4, b, n ;
b = ( n < 0 ? 0 : n * n ) ;
printf ( "\n%d",b ) ;
}

Various logical and arithmetic operators useful in c are give below as:

#include <stdio.h>
#include <math.h>

main() 

 {
  float a, b, c, x1, x2, q, d, x1r, x2r, x1i, x2i;

  printf("Input coefficients of square equation a,b,c:");
  scanf("%f %f %f", &a, &b, &c);
 
  d=b*b -4.0*a*c; 

  if (d > 0)

 {
                                          /* results are real numbers */
          q = pow (d, 1./2);
          x1 = (-b + q)/(2*a);
          x2 = (-b - q)/(2*a);
          printf ("X1=%f   X2=%f\n", x1, x2);
          
        } 

                  else if (d == 0) 

                   {
                                           /* there’s only one result */
                x1 = -b/(2*a);
                printf ("X1=X2=%f\n", x1);

                 } else 

                   {
                                           /* results are complex numbers */
                q = pow(-d, 1./2);
                x1r = -b/(2*a) ;
                x2r = x1r;
                x1i = q/(2*a);
                x2i = -x1i;

                printf ("X1 = (%f,%f)\n", x1r, x1i);
                printf ("X2 = (%f,%f)\n", x2r, x2i);
           }
}

Nested if else means if else into if else i.e. multiple if else statements included in one if else statement.Below is the program demonstrating if else :


/* A demo of nested if-else */
main( )
{
int m ;
printf ( "Enter either 0 or 1" ) ;
scanf ( "%d", &m ) ;
if ( m == 0 )
printf ( "this is zero" ) ;
else
{
if ( m == 1 )
printf ( "this is one" ) ;
else
printf ( "wrong choice" ) ;
}
}

The if account by itself will assassinate a individual statement, or a accumulation of statements, if the announcement afterward if evaluates to true. It does annihilation if the announcement evaluates to false.

SIMPLE IF ELSE PROGRAM :



/* Calculation of gross salary */
main( )
{
float base, gross, da, hra ;
printf ( "Enter basic salary " ) ;
scanf ( "%f", &base ) ;
if (base < 2000 )
{
hra =base * 20 / 100 ;
da = base * 80 / 100 ;
}
else
{
hra = 100 ;
da = base * 90 / 100 ;
}
gross = base + hra + da ;
printf ( "gross salary = Rs. %f", gross ) ;
}

main( )
{
int n ;
printf ( "Enter a number less than 20 " ) ;
scanf ( "%d", &n ) ;
if ( num <= 20 )
printf ( "THIS IS AN ACCURATE PROGRAM" ) ;
}

The keyword if tells the compiler that what follows is a alarm ascendancy instruction. The action afterward the keyword if is consistently amid aural a brace of parentheses. If the condition, whatever it is, is true, again the account is executed. If the action is not accurate again the account is not executed.

Various conditional operators used for if statement are as follows:

• Greater than(>)
• Less than(<)
• Equal to(= =)
• Greater than equla to(>=)
• Less than equal to(<=)
• Not equal to(!=)

Many a times,we would like a set of instructions to be accomplished in situation, and an absolutely altered set of instructions to be accomplished in addition situation. This array of bearings is dealt in C programs application a alarm ascendancy instruction.various decision control stements in C are as follows:

• The if statement 
• The if-else statement
• The conditional operators

There are fundamentally three types of instructions in C:

1. Type Acknowledgment Instruction
2. Arithmetic Instruction
3. Control Instruction

To accomplish the affairs accepted the affairs itself care to ask the user to accumulation the ethics of p, n & r through the keyboard in the coursework of execution. This can be accomplished application a action alleged scanf( ). This action is a counter-part of the printf( ) function. printf( ) outputs the ethics to the awning admitting scanf( ) receives them from the keyboard. This is illustrated in the affairs apparent below:


/* Calculation of simple interest */
main()
{
int a, b;
float c, si ;
printf ( "Enter values of a, b, c" ) ;
scanf ( "%d %d %f", &a, &b, &c ) ;
si = (a * b * c )/ 100 ;
printf ( "%f" , si ) ;
}

Our first C program would simply calculate simple interest for a set of values representing principle, number of years and rate of interest.

/* Calculation of simple interest */
main( )
{
int a, b;
float c, si ;
a = 1000 ;
b = 3 ;
c = 8.5 ;
/* formula for simple interest */
si = (a * b * c) / 100 ;
printf ( "%f" , si ) ;
}

Variable names are names accustomed to locations in memory. These locations can accommodate integer, absolute or appearance constants. In any language, the categories of variables that it can abutment depend on the categories of constants that it can handle. This is because a specific blazon of capricious can authority alone the aforementioned blazon of constant. For example, an accumulation capricious can authority alone an accumulation constant, a absolute capricious can authority alone a absolute connected & a appearance capricious can authority alone a appearance constant.

•  Real constants
•  Integer constants
•  Character constants

• Arrays
• Pointers
• Structures
• Union etc

C is a programming accent developed at AT & T's Bell Laboratories of USA in 1972. It was advised and accounting by a man called Dennis Ritchie. In the backward seventies C began to alter the added accustomed languages of that time like PL/I, ALGOL, etc. No pushed C. It wasn't fabricated the official Bell Labs language. Thus, after any advertisement C's acceptability advance and its basin of users grew. Ritchie seems to accept been afraid that so lots of programmers adopted C to earlier languages like FORTRAN or PL/I, or the newer ones like Pascal and APL. But, that is what happened.