#set document(title: "6.5 Return values", author: "OpenStax / XYZ Homework") #set page(width: 8.5in, height: auto, margin: 1in) #import "@preview/cetz:0.5.2" #set text(font: ("STIX Two Text", "Libertinus Serif", "New Computer Modern"), size: 10.5pt, lang: "en") #show math.equation: set text(font: ("STIX Two Math", "New Computer Modern Math")) #set par(justify: true, leading: 0.62em, spacing: 0.9em) #set enum(spacing: 1.1em) // room between list items so tall inline fractions don't collide #set list(spacing: 1.1em) #set table(stroke: 0.5pt + rgb("#c7ccd3")) #let BLUE = rgb("#183B6F") // brand navy — section bars + example/solution labels (white on navy 11.09:1) #let ORANGE = rgb("#A94509") // brand primary-700 — AA-safe deep orange for TEXT (5.93:1 on white; raw brand #F37021 is 2.94:1 and must never carry text) #let RED = rgb("#DC2626") // brand error-600 #let GREEN = rgb("#059669") // brand success-600 (decoration only; small green text uses green-text #007942) #show heading.where(level: 1): it => block(width: 100%, above: 0pt, below: 16pt, fill: gradient.linear(BLUE, rgb("#2C5AA0")), inset: (x: 14pt, y: 12pt), radius: 3pt, text(fill: white, weight: "bold", size: 19pt, it.body)) #show heading.where(level: 2): it => block(width: 100%, above: 18pt, below: 10pt, fill: BLUE, inset: (x: 10pt, y: 6pt), radius: 2pt, text(fill: white, weight: "bold", size: 12pt, it.body)) #show heading.where(level: 3): it => text(fill: ORANGE, weight: "bold", size: 12.5pt, it.body) #show heading.where(level: 4): it => text(fill: BLUE, weight: "bold", size: 10.5pt, it.body) #let examplebox(label, title, body) = block(width: 100%, breakable: true, fill: rgb("#EFF1F5"), stroke: 0.5pt + rgb("#CFDDF0"), radius: 4pt, inset: 10pt, above: 12pt, below: 12pt)[ #block(below: 6pt)[#box(fill: BLUE, inset: (x: 6pt, y: 2pt), radius: 2pt, text(fill: white, weight: "bold", size: 8.5pt, label)) #h(0.4em) #strong[#title]] #body] // rail = decorative left rule (raw brand token); labelcolor = AA-safe label text shade #let notebox(label, rail, labelcolor, tint, body) = block(width: 100%, breakable: true, fill: tint, stroke: (left: 3pt + rail), inset: (left: 10pt, rest: 8pt), radius: (right: 4pt), above: 11pt, below: 11pt)[ #text(fill: labelcolor, weight: "bold", size: 7.5pt, tracking: 0.5pt)[#upper(label)] #linebreak() #body] #let solutionbox(body) = block(above: 4pt, below: 8pt)[ #text(fill: BLUE, weight: "bold", size: 8.5pt)[Solution] #linebreak() #body] #let figph(msg) = block(width: 100%, height: 60pt, fill: rgb("#f6f7f9"), stroke: (paint: rgb("#c7ccd3"), dash: "dashed"), radius: 4pt, inset: 10pt)[ #align(center + horizon, text(fill: rgb("#889"), style: "italic", size: 9pt, msg))] // Standardize inlined figure sizes: measure the natural CeTZ canvas, then scale to a // consistent envelope (aspect-aware; see build_typst.py FIG_* constants). Unlike the // print preamble, dimensions are FLOORED: in an editor a user can trim a figure to a // degenerate 1-D shape (a bare line), and w/h or tw/w would then divide by zero. #let _STD_W = 3.5 #let _WIDE_W = 5.6 #let _MAX_H = 3.4 #let _ASPECT_WIDE = 2.2 #let _UPSCALE_MAX = 1.15 #let stdfig(body) = context { let m = measure(body) let w = calc.max(m.width / 1in, 0.01) let h = calc.max(m.height / 1in, 0.01) let tw = if w / h > _ASPECT_WIDE { _WIDE_W } else { _STD_W } let s = calc.min(tw / w, _MAX_H / h, _UPSCALE_MAX) align(center, box(scale(x: s * 100%, y: s * 100%, reflow: true, body))) } #show figure: set block(breakable: false) #set figure(gap: 8pt) #show figure.caption: set text(size: 8.5pt, fill: rgb("#555")) == 6.5#h(0.6em)Return values === Learning objectives By the end of this section you should be able to - Identify a function's return value. - Employ return statements in functions to return values. === Returning from a function When a function finishes, the function returns and provides a result to the calling code. A #strong[return statement] finishes the function execution and can specify a value to return to the function's caller. Functions introduced so far have not had a return statement, which is the same as returning None, representing no value. #notebox("Note", rgb("#8a94a6"), rgb("#556666"), rgb("#f7f8fa"))[ #emph[Returning a value from a function] #link("https://www.openstax.org/r/returning-value-from-function")[Returning a value from a function; ch 6, video 11] ] #notebox("Note", rgb("#8a94a6"), rgb("#556666"), rgb("#f7f8fa"))[ #emph[Using return statements] ] === Using multiple return statements Functions that have multiple execution paths may use multiple return statements. Ex: A function with an if-else statement may have two return statements for each branch. Return statements always end the function and return control flow to the calling code. In the table below, calc\_mpg() takes in miles driven and gallons of gas used and calculates a car's miles per gallon. calc\_mpg() checks if gallons is 0 (to avoid division by 0), and if so, returns -1, a value often used to indicate a problem. #figure(table( columns: 2, align: left, inset: 6pt, [def calc\_mpg(miles, gallons):   if gallons \> 0:     mpg = miles/gallons     return mpg   else:     print("Gallons can't be 0")     return -1 car\_1\_mpg = calc\_mpg(448, 16) print("Car 1's mpg is", car\_1\_mpg) car\_2\_mpg = calc\_mpg(300, 0) print("Car 2's mpg is", car\_2\_mpg)], [Car 1's mpg is 28.0 Gallons can't be 0 Car 2's mpg is -1], )) #notebox("Note", rgb("#8a94a6"), rgb("#556666"), rgb("#f7f8fa"))[ #emph[Multiple return statements] ] === Using functions as values Functions are objects that evaluate to values, so function calls can be used in expressions. A function call can be combined with other function calls, variables, and literals as long as the return value is compatible with the operation. #notebox("Note", rgb("#8a94a6"), rgb("#556666"), rgb("#f7f8fa"))[ #emph[Using function calls in expressions] #link("https://www.openstax.org/r/function-calls-in-expressions")[Using function calls in expression; ch 6, video 12] ] #notebox("Note", rgb("#8a94a6"), rgb("#556666"), rgb("#f7f8fa"))[ #emph[Using function values] ] #notebox("Note", rgb("#8a94a6"), rgb("#556666"), rgb("#f7f8fa"))[ #emph[Estimated days alive] Write a function, days\_alive(), that takes in an age in years and outputs the estimated days the user has been alive as an integer. Assume each year has 365.24 days. Use round(), which takes a number and returns the nearest whole number. Then write a main program that reads in a user's age and outputs the result of days\_alive(). Given input: 21 The output is: You have been alive about 7670 days. ] #notebox("Note", rgb("#8a94a6"), rgb("#556666"), rgb("#f7f8fa"))[ #emph[Averaging lists] Write a function, avg\_list(), that takes in a list and returns the average of the list values. \# Define avg\_list() list1 = \[34, 29, 77, 30, 48, 92\] print(list1) print(f"Avg is: {avg\_list(list1):.1f}") list2 = \[4, 2, 12, 8, 8\] print(list2) print(f"Avg is: {avg\_list(list2):.1f}") ]