Type Casting, Command Line Arguments and Defining Constants

Type Casting 

• Type cast is an instruction to the compiler to convert one type into another.

• For example, if you want to store a 'long' value into a simple integer then you can type cast 'long' to 'int'.

• You can convert the values from one type to another explicitly using the cast operator as follows: (type_name) expression

• When a cast involves a narrowing conversion, information might be lost. 

• For example, when casting a long into a short, information will be lost if the long’s value is greater than the range of a short because its high-order bits are removed.

EX:-

#include 

int main() 

{ 

int sum = 17, count = 5; 

double mean;

mean = sum / count; 

printf("Value of mean : %f\n", mean ); 

return 0;

}

#include

int main()

{

int sum = 17, count = 5;

double mean;

mean = (double) sum / count;

printf("Value of mean : %f\n", mean );

 return 0;

 }

Command Line Arguments 

• It is possible to pass some values from the command line to your C programs when they are executed.

• These values are called command line arguments and many times they are important for your program especially when you want to control your program from outside instead of hard coding those values inside the code. 

• The command line arguments are handled using main() function arguments where argc refers to the number of arguments passed, and argv[] is a pointer array which points to each argument passed to the program.

• It should be noted that argv[0] holds the name of the program itself and argv[1] is a pointer to the first command line argument supplied, and *argv[n] is the last argument. 

• If no arguments are supplied, argc will be one, and if you pass one argument then argc is set at 2.

Ex:-

#include 

int main( int argc, char *argv[] ) 

{ 

printf("The first argument supplied is %s\n", argv[0]); 

printf("The second argument supplied is %s\n", argv[1]); 

printf("The third argument supplied is %s\n", argv[2]); 

return 0; 

}

Typical Arithmetic Conversion 

• The typical arithmetic conversions are implicitly performed to cast their values to a common type.

• The compiler first performs integer promotion; if the operands still have different types, then they are converted to the type that appears highest in the given hierarchy.

int- unsigned int- long- unsigned long- long long- unsigned long long- float- double- long double

• In any program it is recommended to only perform arithmetic operations on pairs of values of the same type.

• For widening conversions, the numeric types, including integer and floating-point types, are compatible with each other. 

• There are no automatic conversions from the numeric types to char or boolean. Also, char and boolean are not compatible with each other.

Ex:

#include 

int main (void) 

{ 

float f1 = 123.125, f2; 

int i1, i2 = -150; 

char c = 'a'; /* floating to integer conversion */ i1 = f1; 

printf ("%f assigned to an int produces %i\n", f1, i1); /* integer to floating conversion */ f1 = i2; 

printf ("%i assigned to a float produces %f\n", i2, f1); 12  /* integer divided by integer */ f1 = i2 / 100; 

printf ("%i divided by 100 produces %f\n", i2, f1); /* integer divided by a float */ f2 = i2 / 100.0; 

printf ("%i divided by 100.0 produces %f\n", i2, f2); /* type cast operator */ f2 = (float) i2 / 100; 

printf ("(float) %i divided by 100 produces %f\n", i2, f2); 

return 0; 

}

Defining Constants 

• There are two ways to define constant in C programming:  
• Using the const key word. 

const data_type constant_name = constant_value; const float PI = 3.1412; 

• Using the #define directive. 
• #define come before the program main block. 

#define constant_name constant_value

#define PI 3.1412 

Ex:-

#include 

int main () 

{ 

const float PI = 3.1412; 

float radius; 

printf ("Enter the radius in mm : \n"); 

scanf ("%f",&radius); 

printf("The perimeter is : %.2f", 2*PI*radius); 

return 0; 

} 

Math Functions 

• The math.h header defines various mathematical functions.

Here some examples;

1 - double asin(double x) Returns the arc sine of x in radians. 

2 - double atan(double x) Returns the arc tangent of x in radians. 

3 - double atan2(double y, double x) Returns the arc tangent in radians of y/x based on the signs of both values to determine the correct quadrant.