Pseudocode with filters, if–else and nested conditions

A while chooses whether to repeat a block. An if chooses whether to execute a block during this visit. An else chooses the alternative when that particular if condition is false.

Put the update inside the right filter #

FSum = 0
while (Pile1 has cards) {
    Read top card X
    Move X to Pile2
    if (X.Gender == "F") {
        FSum = FSum + X.Mathematics
    }
}

Every card is still visited. Only F cards update FSum. With the supplied Scores table, FSum=951; the M sum is 1220. Use an if/else split only when valid records are known to have exactly the two expected labels, or add explicit handling for other values.

A nested filter can become AND when only the matching action matters #

if (X.CityTown == "Chennai") {
    if (X.Gender == "F") { Count = Count + 1 }
}

Equivalent matching action:
if (X.CityTown == "Chennai" AND X.Gender == "F") {
    Count = Count + 1
}

Both forms count only Chennai F records. In the supplied table, the count is 5. The indentation and braces make it clear that the inner test is inside the city filter.

An else can make the same rewrite wrong #

Original:
if (X.CityTown == "Chennai") {
    if (X.Gender == "F") { FCount = FCount + 1 }
    else { MCount = MCount + 1 }
}

NOT equivalent:
if (X.CityTown == "Chennai" AND X.Gender == "F") {
    FCount = FCount + 1
}
else { MCount = MCount + 1 }

In the original, non-Chennai records update neither count. In the rewrite, every record that is not both Chennai and F updates MCount, including Madurai F records. The else negates the entire combined condition, not just the gender test.

Safe alternatives #

Keep the nested structure, or use complete independent filters: Chennai AND F for FCount; Chennai AND M for MCount. The supplied table has five Chennai F records and three Chennai M records. Both totals together account for Chennai’s eight scorecards.

Reuse the structure for a maximum #

Replace the fixed group filter by X.Mathematics > Max, and replace addition by Max = X.Mathematics. Seed safely, then add owner updates if needed. A sum and a maximum can share a loop shape while requiring different initialization and different update rules.

Source: Lecture 2.10; Tutorial 2.8. Small teaching datasets and diagrams are prepared for these notes; lecture and tutorial totals are identified explicitly.