Simple C random lottery number

Question

I would like to generate 5 different numbers in the simplest way and put them into an array. Something is wrong with my way of thinking, could you please correct my code?

void lottery(int *array){
    int i = 0;
    while(i != 5){
        bool good = true;
        int number = rand()%90+1;
        for(int j=0; j<5; j++){
            if(array[j] == number)
                good = false;
                break;

        }
        if(good){
            array[i] == number;
            i = i+1;
        }
    }
}

int main(){
    srand(time(0));
    int numbers[5];
    lottery(numbers);

    for(int i =0; i<5; i++){
        printf("%d, ",numbers[i]);
    }
    return 0;
}

`array[i] == number` also consider that your array is not initialized. — kingW3, Oct 22 '18 at 22:17
Change `j < 5` to `j < i`. You know the array only contains `i` values. — rici, Oct 22 '18 at 22:25
In the future, never give only “something is wrong” as a problem description. Show sample output that is wrong and either say precisely what is wrong with it or show sample output that would be right, or both. Usually, you should also show sample input that produces the sample output. When `srand` is involved, you should both show the seed used (change it from `time(0)` to a constant, and try different constants until you find one that produces a sample to show) and show the values produced by each `rand` call (because different C implementations have different `rand` implementations). — Eric Postpischil, Oct 22 '18 at 22:32
`==` is not the assignment operator. It is not a matter of your "way of thinking", just a typo. — Clifford, Oct 22 '18 at 22:43
Do you realize that the break in `if(array[j] == number) good = false; break;` is unconditionally breaking the `for` loop — C is not Python and indentation means nothing to the compiler and a lot to the humans reading C. You need braces around the assignment and break. — Jonathan Leffler, Oct 22 '18 at 22:54

score 2 · Accepted Answer · answered Oct 22 '18 at 22:54

Including the findings of kingW3 and rici and cleaning it up a little:

// compiles without errors with:
// clang -O3 -g3 -Weverything -W -Wall -Wextra -Wpedantic -fsanitize=bounds  -std=c11  -o stacktest stacktest.c 
#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#include <time.h>

void lottery(int *array);
void lottery(int *array){
    int i = 0;
    while(i != 5){
        bool good = true;
        int number = rand()%90+1;
        // limit is 'i' because you fill the array in order
        for(int j=0; j<i; j++){
            // Would always `break` without the curly brackets
            if(array[j] == number){
                good = false;
                break;
            }
        }
        if(good){
            // Use '=' instead of '=='
            array[i] = number;
            i = i+1;
        }
    }
}

int main(void){
    // time returns type 'type_t', needs casting to get rid of
    // warning
    srand( (unsigned int) time(0));
    // return of rand() is always >= 0, so 
    // initialize with a negative number
    int numbers[5] = {-1};
    int i;
    lottery(numbers);
    for(i =0; i<4; i++){
        printf("%d, ",numbers[i]);
    }
    printf("%d\n",numbers[i]);
    return 0;
}

The missing brackets were another error.

Caveat: time() has most probably a resolution of one second, so don't run it too fast in sequence or you'll get the same numbers.

Simple C random lottery number

1 Answers1