All programming languages provide access to a large collection
of subprograms for common tasks such as computing square roots
and other mathematical functions, performing input and output,
sorting lists, etc. The only difference is in how this functionality
is provided.
An *intrinsic*, or built-in function is
a function that is recognized by the compiler. Functions can
also be provided by libraries that are separate from the compiler.

Unlike many languages, C has *no* intrinsic
functions. All functions in C are provided by libraries,
separate from the compiler.
The interface (required arguments and return values) of common
functions such as `printf()`

, `sin()`

,
`cos()`

, `exp()`

, etc. are specified
in header files such as `stdio.h`

and
`math.h`

and the functions themselves
are provided by precompiled libraries such as
`libc.so`

and `libm.so`

.

The function interface comes in the form of a
*prototype*, which simply states the
return type and the type of each argument the function requires:

shell-prompt: fgrep 'sin(' /usr/include/math.h double asin(double); double sin(double);

To use `printf()`

in a C program, we must add
the line
`#include <stdio.h>`

. To use `sin()`

and other math functions, we must add
`#include <math.h>`

and use `-lm`

to link with the standard math library.

To find out which header files and/or libraries are required for a given C library function, and what the interface looks like, simply check the man page:

shell-prompt: man sin SIN(3) FreeBSD Library Functions Manual SIN(3) NAME sin, sinf, sinl sine functions LIBRARY Math Library (libm, -lm) SYNOPSIS #include <math.h> double sin(double x); float sinf(float x); long double sinl(long double x); DESCRIPTION The sin(), sinf(), and sinl() functions compute the sine of x (measured in radians). A large magnitude argument may yield a result with little or no significance. RETURN VALUES The sin(), sinf(), and sinl() functions return the sine value. SEE ALSO acos(3), asin(3), atan(3), atan2(3), cos(3), cosh(3), csin(3), math(3), sinh(3), tan(3), tanh(3) STANDARDS These functions conform to ISO/IEC 9899:1999

One of the best ways to become a great C programmer is by browsing the header files. This is how you discover all the cool features that are available to make your life easier. As a new C programmer, there will be things in the header files that you don't understand. Ignore them if you don't have time to explore them right now, and just take in what comes easily for now.

shell-prompt: more /usr/include/math.h [scroll past stuff that's Greek to you] #define M_E 2.7182818284590452354 /* e */ #define M_LOG2E 1.4426950408889634074 /* log 2e */ #define M_LOG10E 0.43429448190325182765 /* log 10e */ #define M_LN2 0.69314718055994530942 /* log e2 */ #define M_LN10 2.30258509299404568402 /* log e10 */ #define M_PI 3.14159265358979323846 /* pi */ #define M_PI_2 1.57079632679489661923 /* pi/2 */ #define M_PI_4 0.78539816339744830962 /* pi/4 */ #define M_1_PI 0.31830988618379067154 /* 1/pi */ #define M_2_PI 0.63661977236758134308 /* 2/pi */ #define M_2_SQRTPI 1.12837916709551257390 /* 2/sqrt(pi) */ #define M_SQRT2 1.41421356237309504880 /* sqrt(2) */ #define M_SQRT1_2 0.70710678118654752440 /* 1/sqrt(2) */ #define MAXFLOAT ((float)3.40282346638528860e+38) [scroll down more] int isinf(double); int isnan(double); double acos(double); double asin(double); double atan(double); double atan2(double, double); double cos(double); double sin(double); double tan(double); double cosh(double); double sinh(double); double tanh(double); double exp(double); double frexp(double, int *); /* fundamentally !__pure2 */ double ldexp(double, int); double log(double); double log10(double); double modf(double, double *); /* fundamentally !__pure2 */ double pow(double, double); double sqrt(double); double ceil(double); double fabs(double) __pure2; double floor(double); double fmod(double, double); [and much more...]

Functions are subprograms which are called by using them within an expression, and for the most part, look like they would in any algebraic expression. The general form is

function-name(argument [, argument ...])

An *argument* is any value that we pass
to the function, such as the angle required by the sine, cosine,
and tangent functions. The function call itself is an expression
that has the value returned by the function. For example,
the value of the expression `sin(M_PI)`

in a C program
is 0.0, since the sine of any multiple of Pi is 0.

#include <stdio.h> // For printf() #include <math.h> // For sin() and M_PI int main() { printf("The sine of %f is %f\n", M_PI, sin(M_PI)); return 0; }

In the code above, `M_PI`

is an argument to the
`sin()`

function, and
`"The sine of %f is %f\n"`

and
`sin(M_PI)`

are arguments to `printf()`

.

To compile this code, we can use the following:

cc -O sine-pi.c -o sine-pi -lm

Fortran provides a wealth of intrinsic mathematical functions for computing trigonometry functions, logarithms, etc. The complete list of functions is too extensive to list here, but it includes all the standard trigonometric functions, square root, etc.

module constants double precision, parameter :: PI = 3.1415926535897932d0 end module constants program sine_pi print *, 'The sine of ', PI, ' is ', sin(PI), '.' end program

Fortran can also utilize addition functions from external libraries, as C does.

What is an intrinsic function?

How many intrinsic (built-in) functions does the C language have? Elaborate.

What is a prototype in C?

Where do we find prototypes for C standard library functions such as sin()?

How would we find out which header files and libraries are required for the sqrt() function?

What is an argument?

What is a return value?

How do we call a function?

How many intrinsic functions for Fortran have?

Is Fortran limited to intrinsic functions only?