Introductory Programming Examples A Simple Welcome Program greet

Introductory Programming Examples

A Simple Welcome Program greet !every program has a name !execution of this program results in the display of !of the welcome message implicit none !compiler directives or declarations !this is legacy; ALWAYS include this line in your program print * , "Hi! Welcome to the session“ !body with just one statement end program greet

Execution of the Program • To execute the program – First compile the program f 90 –o greet. f 90 – This results in an executable greet – Run greet (invoke in the command line) • When greet is run, it prints Hi! Welcome to the session

A More interesting program Program greet 1 implicit none character(len = 20): : name !name - variable that stores character string of length less than or equal to 20 print *, "Hi! Welcome to the session“ print *, "PL. tell me your name“ read *, name !waits for the user to give a character string !this string is then stored in "name“ print *, "Hi, ", name print *, "How are you“ end greet 1

Some Observations • Print and Read statements • Variables high level abstractions of memory • Variables store values input by you • Stored values can be read back and printed • Values are character strings

Behavior of greet 1 • Compile and execute the object file • It first prints Hi! Welcome to the session PL. tell me your name • It then waits for you to input the name • The input string(Hari), is read into name • Finally it prints Hi! Hari How are you?

Another variation program greet 2 !asks for first and surname implicit none character(len = 10): : first_name, sur_name ! two variables are declared character(len = 20): : full_name !another variable of length 20 print *, "Hi! Welcome to the session“ print *, "PL. tell me your first name“

Program Continued !waits for the user to give a character string read *, first_name read *, sur_name full_name = first_name//" "//sur_name !assignment statement !rhs is an expression which is evaluated !resulting value is stored in lhs variable !// is string concatenation operator print *, "Hi, ", full_name, " How are you“ end greet 2

A Problem • Examine the output of the above program, when the input is given as Dinesh Mongia • the program will outputs Dinesh Mongia • There are 4 blank spaces after `Dinesh' (why? ) • How do we remove the blanks? • Here is the program

A Solution program greet 3 implicit none character(len = 10): : first_name, sur_name character(len = 20): : full_name print *, "Hi! Welcome to the session“ print *, "PL. tell me your first name“ read *, first_name read *, sur_name full_name = trim(first_name)//" "//trim(sur_name) !trim is an intrinsic function that removes trailing blanks print *, "Hi, ", full_name, " How are you“ end greet 3

A simple arithmetic function Program sum_and_multiply implicit none integer : : x, y, sum, prod !declaration of integer variables read *, x, y sum = x + y !value in x and y are added and stored in sum prod = x * y print *, "Sum of ", x, " and ", y, " is = ", sum print *, "Product of ", x, " and ", y, " is = ", prod end program sum_and_multiply

Another Simple Program convert_to_seconds implicit none integer : : hour, minute, in_second, out_second read *, hour, minute, in_second out_second = out_second + (minute * 60) out_second = out_second + (hour * 60) print *, out_second end program convert_to_seconds

Observation • Complex algebraic expressions allowed on the right hand side of assignment statement • Same variable can appear both in the right hand left hand sides • Rhs occurrence refers to the current content • Lhs occurrence refers to the location

Interest Calculation Program interest implicit none real: : principle, year, rate, inter, total !declaration of real variable read *, principle, year, rate inter = (principle*year*rate)/100 total = principle + inter print *, inter, total end program interest How to compute compound interest?

Distance Calculation program pt_distance !computes distance between two pts. implicit none real : : a, b, c, d, distance !Two points are (a, b) and (c, d) print * , "type values of a, b, c, d“ read * , a, b, c, d distance = sqrt((a - c) ** 2+(b - d) ** 2) !sqrt intrinsic function on real values; argument an expn. print * , "distance between points (", a, & ", ", b, ") and (", c, ", ", d, ") is", distance !note & at the end of first line – denotes Continuation !length of a line can not exceed 132 characters end program point_distance