Functions Handout

Subroutines
In computer science, a subroutine (also called procedure, method, function, or routine) is a portion
of code within a larger program that performs a specific task and is relatively independent of the
remaining code. The big advantage of a subroutine is that it breaks a program into smaller, easier
to understand pieces. It also makes debugging easier. A subroutine can also be reused in another
program.
The basic idea of a subroutine is that it will take various values, do something with them, and return
a result. In most languages (including all the ones we use in this class) the variables in a subroutine
are local. That means that they do not affect anything outside the subroutine.
Below are three examples in three different languages of a subroutine that solves the equation:
f(x,y) = x 2 sin(y)
In each example the name of the subroutine is george. The subroutine george takes two arguments
x and y, and returns the value of the equation to the main program. In the main program a
variable named junk is assigned the value returned by george. Notice that in the main program the
subroutine george is called using the arguments a and b. Since the variables in the subroutine are
local, you do not have name them x and y in the main program.
AWK
function george(x,y)
{
result = x^2 * sin(y)
return result
}
# Main Part of Program
BEGIN{OFS="\t"}
{
}
END{}
a = 1.2
b = 3.4
junk = george(a,b)
print junk

IDL
FUNCTION george, x, y
END
result = x^2 * sin(y)
return,result
IDL> .run george
IDL> a = 1.2
IDL> b = 3.4
IDL> junk = george(a,b)
IDL> print,junk
Python
def george(x,y):
result = x**2 * sin(y)
return result
# Main Part of Program
def main():
a = 1.2
b = 3.4
junk = george(a,b)
print junk
if __name__ == "__main__":
main()