Tossing a Die in C Until We Get a 6

Track every roll of a die in C: print as we go, store the history in an array, tally frequencies, and list which steps produced each face.

Code 10 min

By the end of this lesson you will

• Simulate tossing a die until a 6 appears
• Store the history in an array and tally frequencies

Resources

• rand
• Arrays

We are going to toss a die and track every output, while waiting for 6 to appear.

We keep rolling the die until it shows 6.

New to srand(time(NULL))? See why it seeds the generator first. Each program below is hidden by default. Try it yourself first: open See hint if we get stuck, and press Reveal to check our answer.

Track Every Roll

The simplest approach is to print inside the loop. This shows each roll as it happens:

• Seed the generator once: srand(time(NULL)).
• Start with dice = 0 and count = 0.
• Repeat while dice != 6:
• Roll: dice = rand() % 6 + 1.
• Add 1 to count.
• printf the step number and the roll.
• After the loop, print count.

#include <stdio.h>
#include <stdlib.h>
#include <time.h>

int main(void) {
    srand(time(NULL));

    int dice = 0;
    int count = 0;

    while (dice != 6) {
        dice = (rand() % 6) + 1;
        count++;
        printf("Step %d: rolled %d\n", count, dice);
    }

    printf("We have 6, in %d steps.\n", count);
    return 0;
}

Example output:

Step 1: rolled 3
Step 2: rolled 1
Step 3: rolled 5
Step 4: rolled 6
We have 6, in 4 steps.

This is the fastest way to see each value. But it prints as it goes — you can’t review the sequence afterward, and the numbers scroll past.

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Better: Store the Rolls in an Array

If you want to keep the full history and print it at the end (e.g., to analyze it), use an array:

• Make an array rolls[100] and set count = 0, dice = 0.
• Repeat while dice != 6 and count < 100:
• Roll the die.
• Save it: rolls[count] = dice.
• Add 1 to count.
• After the loop, a for loop from 0 to count - 1 prints each stored roll.
• Print count.

#include <stdio.h>
#include <stdlib.h>
#include <time.h>

int main(void) {
    srand(time(NULL));

    int rolls[100];   // assume no more than 100 rolls
    int count = 0;
    int dice = 0;

    while (dice != 6 && count < 100) {
        dice = (rand() % 6) + 1;
        rolls[count] = dice;
        count++;
    }

    printf("Roll history: ");
    for (int i = 0; i < count; i++) {
        printf("%d", rolls[i]);
        if (i < count - 1) printf(", ");
    }
    printf("\n");

    printf("We have 6, in %d steps.\n", count);

    return 0;
}

Example output:

Roll history: 3, 1, 5, 6
We have 6, in 4 steps.

Why the count < 100 check? If rand() somehow never returns 6 (theoretically possible, practically absurd), the loop would run forever and overflow the array. This guards against that.

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Even Better: Tally the Frequencies

If your goal is to know how many times each number appeared, use an array indexed by the value:

• Make frequencies[7], all zeros (index 0 unused).
• Repeat while dice != 6:
• Roll the die.
• Tally it: frequencies[dice]++.
• Add 1 to count.
• After the loop, a for from face 1 to 6 prints frequencies[face].
• Print count.

#include <stdio.h>
#include <stdlib.h>
#include <time.h>

int main(void) {
    srand(time(NULL));

    int frequencies[7] = {0};   // index 0 unused; counts for 1-6
    int count = 0;
    int dice = 0;

    while (dice != 6) {
        dice = (rand() % 6) + 1;
        frequencies[dice]++;
        count++;
    }

    printf("Roll frequencies:\n");
    for (int face = 1; face <= 6; face++) {
        printf("  %d: %d times\n", face, frequencies[face]);
    }
    printf("Total rolls: %d\n", count);

    return 0;
}

Example output:

Roll frequencies:
  1: 2 times
  2: 0 times
  3: 1 times
  4: 0 times
  5: 1 times
  6: 1 times
Total rolls: 5

This is the pattern used constantly in data analysis — counting occurrences per category. In R this is table(); in Python it’s collections.Counter(); in C you build it yourself with an array.

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The Note About frequencies[7]

You’ll notice the array is size 7, not 6. That’s because array indices in C start at 0, but dice faces are 1–6. So we waste index [0] and use indices [1] through [6]. This is a small, harmless price for readable indexing.

The alternative — frequencies[dice - 1] — packs the array to size 6 but means every access has a -1 in it. Both are common; I prefer the size-7 version for clarity.

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Finally: Which Steps Gave Each Face?

Now we want more than counts: for each face, which steps produced it? We store the rolls in an array, then scan the array once per face and print the step numbers that match.

• Store every roll in rolls[] as before; keep count.
• For each face from 1 to 6:
• Print the face.
• Scan step from 0 to count - 1.
• If rolls[step] == face, print step + 1.
• Print a newline before the next face.

#include <stdio.h>
#include <stdlib.h>
#include <time.h>

#define MAX_ROLLS 100

int main(void) {
    srand(time(NULL));

    int rolls[MAX_ROLLS];
    int count = 0;
    int dice = 0;

    while (dice != 6 && count < MAX_ROLLS) {
        dice = (rand() % 6) + 1;
        rolls[count] = dice;
        count++;
    }

    for (int face = 1; face <= 6; face++) {
        printf("%d:", face);
        for (int step = 0; step < count; step++) {
            if (rolls[step] == face) {
                printf(" %d", step + 1);
            }
        }
        printf("\n");
    }

    return 0;
}

Example output:

1: 2
2: 3 4
3: 5
4:
5: 1
6: 6

Read it as: the first roll was a 5, the second a 1, the third and fourth were 2s, the fifth a 3, and the sixth finally gave the 6. A face that never appeared (here, 4) just gets an empty list.

The outer loop picks a face and the inner loop scans the history, so the work is 6 × count comparisons. That is nothing for a die, but for many categories you would tally in one pass instead, as in the frequency array above.

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Which Approach to Choose?

Goal	Use
Just see each roll as it happens	printf inside the loop
Store history to review/analyze later	Array of rolls
Count how often each face appears	Frequency array
Both history and frequency	Combine: store rolls in one array, tally in another
Which steps produced each face	Store the rolls, then scan once per face

• Store every roll in an array to analyse the run afterwards.
• A frequency array counts how often each face appeared.
• Index 1 to 6 means the array needs 7 slots.

Frequency. How many times a value occurred in the data.