Python solution

def menu():

    allStudentMarks = {}  #Storage for all students marks. The storage is in the form of a dictionary data structure

    while True:

        kbinput = input("Enter 1 to store student details\n" +

                    "Enter 2 to display student report\n" +

                    "Enter any other key to exit\n")

        if kbinput == '1':

                allStudentMarks = enterAllMarksOfAStudentToStorage(allStudentMarks)

        elif kbinput == '2':

                displayAllReports(allStudentMarks)

        elif kbinput!='1' and kbinput != '2':

            break #break could have been replaced by return. return returns the control flow out of the function

                    #break breaks the control out of the loop

def enterAllMarksOfAStudentToStorage(allStudentMarks):

    while True:

        fname = input("Enter a student's full name\n")

        if searchStudentMarks(fname,allStudentMarks ):

            print(fname, " already exists in the system. Choose another name\n")

        else:

            break

    #enter valid marks for DF Report; valid marks range: 0 to 20

    while True:

        dfReportMarks = input("enter marks for DF Report; valid marks range: 0 to 20\n")

        dfReportMarks = float (dfReportMarks)

        if dfReportMarks >= 0 and dfReportMarks <= 20:

            break

    #enter valid makrs for Project: valid marks range: 0 to 30

    while True:

        projectMarks = input("enter marks for Project; valid marks range: 0 to 30\n")

        projectMarks = float (projectMarks)

        if projectMarks >= 0 and projectMarks <= 30:

            break

    while True:

        finalExamMarks = input("enter marks for Final Exam; valid marks range: 0 to 50\n")

        finalExamMarks = float (finalExamMarks)

        if finalExamMarks >= 0 and finalExamMarks <= 50:

            break

    studentMarks = [dfReportMarks, projectMarks, finalExamMarks]

    allStudentMarks[fname] = studentMarks

    ##temporary code to display current dictionary content

    for k, v in allStudentMarks.items():

        print ("Student ", k, "'s marks are \n")

        for m in v:

            print(m, "\t")

    return allStudentMarks

def displayAllReports(allStudentsDetails):

    kbinput = int (input("Enter 1 to get DF Report Marks\n" +

            "Enter 2 to get Project Marks\n" +

            "Enter 3 to get Final Exam Marks\n" +

            "Enter 4 to get Overall Marks\n" +

            "Enter 5 to get Selected Student Marks\n" +

            "Enter 6 to get to Menu\n"))

    if kbinput == 1:

            belowDFAvgDetails = getBelowAvgDFReportMarksReport(allStudentsDetails)

            displaySelectedStudentsMarks(belowDFAvgDetails)

    if kbinput == 2:

             getBelowAvgProjectMarksReport()

    if kbinput == 3:

            getBelowAvgFinalExamMarksReport()

    if kbinput == 4:

            getBelowAvgOverallMarksReport()

    if kbinput == 5:

            displaySelectedStudentsMarks()

    if kbinput == 6:

            return

def displayAStudentsDetail(aDict):  #1

        displayADictionary(aDict)     #2

def displayAList(aListToDisplay):   #3                            

    print("The marks are in following order: 'DF Report Marks' 'Project Marks' and 'Final Exam Marks'")      #4

    for anItem in aListToDisplay:  #5

        print(anItem, end=' ')   #6

def displayADictionary(aDict):      #7

        for k,v in aDict.items():     #8

            print(k, " ", end=" ")  #9

            displayAList(v)         #10

            print()                 #11

def getBelowAvgDFReportMarksReport(aDictionary): #12

        sumOfDFMarks = 0                           #13

        for aVal in aDictionary.values():          #14

                sumOfDFMarks = sumOfDFMarks + aVal[0]#15

        avg = sumOfDFMarks/len(aDictionary)        #16

        belowDFAvgDict = {}                        #17

        for k, v in aDictionary.items():           #18

            if avg> v[0]:                        #19

                belowDFAvgDict[k] = v          #20

            return ["Below Avg DF Mark: ", avg, belowDFAvgDict] #21

def displaySelectedStudentsMarks(aList):         #22

        print(aList[0],aList[1] )                  #23

        displayADictionary(aList[2])               #24

def getBelowAvgProjectMarksReport():

    print("The  getBelowAvgProjectMarksReport got invoked\n")

def getBelowAvgFinalExamMarksReport():

    print("The getBelowAvgFinalExamMarksReport got invoked\n")

def getBelowAvgOverallMarksReport():

    print("The getBelowAvgOverallMarksReport got invoked\n")

def displaySelectedStudentsMarks():

    print("The displaySelectedStudentsMarks got invoked\n")

def searchStudentMarks(newNameOfStudent, allStudentsStorage):

    return  newNameOfStudent in allStudentsStorage

menu()