#
# Unit 6 - User-functions
#
# Practice
#

# Main focus on structure. 
# Additional revision of previous study material. 

# (1)
# Write the function Q1. 
# The function has two parameters: 
#   x and y, both numeric values. 
# The function returns their average
Q1 <- function(x, y) {
  return ((x + y) / 2)
}

print(Q1(5, 3))



# (2)
# Write the function Q2. 
# The function has two parameters: 
#   x and y, both numeric values. 
# The function returns their multiplication, 
# without using the * operator. 
Q2 <- function(x, y) {
  result <- 0 
  for (i in 1:y) {
    result <- result + x 
  }
  return (result)
}

print(Q2(7, 6))

5 + 5 + 5




 
 
# (3)
# Write the function Q3. 
# The function has two parameters: 
#   x and y, both numeric values. 
# The function returns the bigger of the two. 
Q3 <- function(x, y) {
  if (x > y) {
    return (x)
  } 
  if (x < y) {
    return (y)
  } 
  return (x)
}
 
print(Q3(8, 9))

 
# (4)
# Write the function Q4. 
# The function has one parameter: 
# grades - a non-empty vector. 
# The function produces a new vector, 
# in which 5 is added to each of vec's grade 
# which is bigger than 90, and each grade 
# greater than 95 is rounded to 100. 
# The function returns the new vector. 
# 1
Q4 <- function(grades) {
  newGrades <- c() 
  for (ind in 1:length(grades)) {
    curGrade <- grades[ind]
    if (curGrade > 90 & curGrade <= 95) {
      newGrades <- c(newGrades, grades[ind] + 5) 
    } else if (curGrade > 95) {
      newGrades <- c(newGrades, 100) 
    } else {
      newGrades <- c(newGrades, grades[ind])
    }
  }
  return (newGrades)
}

myGrades <- c(99, 94, 75, 22) 
print(Q4(myGrades))

# 2
Q4 <- function(grades) {
  newGrades <- c() 
  for (ind in 1:length(grades)) {
    curGrade <- grades[ind]
    if (curGrade > 90 & curGrade <= 95) {
      newGrades[ind] <- grades[ind] + 5
    } else if (curGrade > 95) {
      newGrades[ind] <- 100 
    } else {
      newGrades[ind] <- grades[ind]
    }
  }
  return (newGrades)
}

myGrades <- c(99, 94, 75, 22) 
print(Q4(myGrades))

vec <- c() 
vec[1] <- 2
vec[2] <- 5
vec[3] <- 9
print(vec)


# (5)
# Write the function Q5. 
# The function has three parameters: 
# x and y - numeric values, 
# op - 1 (default), or 0. 
# If op equals 1 the functions 
# returns x + y, and if it is 0
# the function returns x - y. 
Q5 <- function(x, y, op = 1) {
  if (op == 1) {
    return (x + y)
  }
  return (x - y)
}

print(Q5(3, 4, 0))

 
# (6)
# Write the function Q6. 
# The function has two parameters: 
# - vec - a vector 
# - inds - a vector of indices in vec 
# The function  produces a new vector
# including all values in vec whose indices 
# are listed in inds, and in their order in the latter. 
# The function returns the new vector. 
Q6 <- function(vec, inds) {
  result <- c() 
  for (ind in inds) {
    result <- c(result, vec[ind])
  }
  return (result)
} 

myVec <- c(5, 4, 3, -1, 6)
myInds <- c(5, 1, 3)
print(Q6(myVec, myInds))


# (7)
# Write the function Q7
# The function has one parameter: 
# - vec - a non empty vector
#         including more than 3 values,
# The function iteratively and reandomly produces 
# an index in vec.
# When the same index is chosen
# twice, the function returns 
# the value in that index
# 1
Q7 <- function(vec) {
  chosen <- c()
  while (TRUE) {
    randInd <- sample(1:length(vec), size = 1)
    print(randInd)
    if (!randInd %in% chosen) {
      chosen <- c(chosen, randInd)
    } else {
      return (vec[randInd])  
    }
  }
}

myVec <- c(5, 4, 2, 3)
print(Q7(myVec))

# 2
Q7 <- function(vec) {
  chosen <- c()
  found <- TRUE
  while (found) {
    randInd <- sample(1:length(vec), size = 1)
    print(randInd)
    if (randInd %in% chosen) {
      found <- FALSE
    } else {
      chosen <- c(chosen, randInd)
    }
  }
  return (vec[randInd])
}

myVec <- c(5, 4, 2, 3)
print(Q7(myVec))