Taking Input in Arrays — Read

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One extraction fills exactly one array position

Suppose scores has five positions and i currently equals 2. The statement cin >> scores[i] consumes one integer from the input and stores it at scores[2]. It does not fill scores[0], scores[1], scores[3], or scores[4]. The subscript scores[i] selects one destination for that one extraction.

CPPWith i equal to 2, one extraction writes to scores[2].

const int n = 5;
int scores[n];
int i = 2;

cin >> scores[i];

If the next typed value is 19, the result of this statement is that scores[2] becomes 19. The other positions are not filled by that statement. To fill all five positions, you need five extractions and a way to change the destination between them.

CHECKPOINT 1Not answered

Given i = 2 and an extraction that consumes 19, which position receives the value?

Checkpoints are not graded. They are here so you catch yourself before the quiz does — stuck, ask the tutor on the right.

Changing the index after every read fills the whole array

An indexed for loop performs one extraction for each value of i from 0 through 4. On every iteration, cin >> scores[i] consumes the next integer and sends it to the position named by the current i. The loop condition i < n gives five iterations because n is 5.

CPPThe changing index gives each extraction its destination.

const int n = 5;
int scores[n];

for (int i = 0; i < n; i++) {
    cin >> scores[i];
}

ITERATION	CONSUMED VALUE	DESTINATION	ARRAY AFTER THE WRITE
i = 0	12	scores[0]	[12, _, _, _, _]
i = 1	7	scores[1]	[12, 7, _, _, _]
i = 2	19	scores[2]	[12, 7, 19, _, _]
i = 3	4	scores[3]	[12, 7, 19, 4, _]
i = 4	10	scores[4]	[12, 7, 19, 4, 10]

Five extractions produce the final contents of scores.

The five values are not placed into scores all at once. The loop performs five separate extractions: 12 goes to scores[0], 7 goes to scores[1], 19 goes to scores[2], 4 goes to scores[3], and 10 goes to scores[4]. The final state is scores = [12, 7, 19, 4, 10].

Each extraction consumes one value and stores it at scores[i].

CHECKPOINT 2Not answered

Complete the subscript so this loop reads five values into indices 0-4.

for (int i = 0; i < n; i++) {
    cin >> scores[?];
}

Checkpoints are not graded. They are here so you catch yourself before the quiz does — stuck, ask the tutor on the right.

Spaces and line breaks separate values without changing their destinations

For integer input, spaces and line breaks both separate one value from the next. These separators do not choose array positions. The loop still decides the destination with scores[i], so the input 12 7 19 4 10 produces the same array whether all five values appear on one line or each value appears on a separate line.

CPPWhitespace separates integer tokens, while i selects their destinations.

const int n = 5;
int scores[n];

for (int i = 0; i < n; i++) {
    cin >> scores[i];
}

// The following input layouts have the same result:
// 12 7 19 4 10
//
// 12
// 7
// 19
// 4
// 10

The first extraction always takes the first integer token, the second takes the next token, and so on. With either layout, the first token 12 reaches scores[0], the third token 19 reaches scores[2], and the last token 10 reaches scores[4]. The final state remains scores = [12, 7, 19, 4, 10].