Question

How to generate 20 digits random number in C

Answer 1

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

typedef struct {
    char digits[21]; // 20 digits + null terminator
} BigDecimal;

BigDecimal generate20DigitsRandomNumber() {
    BigDecimal dec;
    srand(time(NULL));
    
    for (int i = 0; i < 20; i++) {
        dec.digits[i] = (rand() % 9) + '1'; // Generate digits from '1' to '9'
    }
    
    dec.digits[20] = '\0'; // Null-terminate the string

    return dec;
}

int main() {
    BigDecimal number = generate20DigitsRandomNumber();
    
    printf("%s\n", number.digits);
    
    return 0;
}



/*
run:

95282522322662942458

*/

 

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Answer 2

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

typedef struct {
    char digits[21]; // 20 digits + null terminator
} BigDecimal;

long double generate20DigitsRandomNumber() {
    BigDecimal dec;
    srand(time(NULL));
    
    for (int i = 0; i < 20; i++) {
        dec.digits[i] = (rand() % 9) + '1'; // Generate digits from '1' to '9'
    }
    
    dec.digits[20] = '\0'; // Null-terminate the string

    long double ld;
      
    return strtold(dec.digits, NULL);
}

int main() {
    long double number = generate20DigitsRandomNumber();
    
    printf("%.0Lf\n", number);
    
    return 0;
}



/*
run:

99742712572439565688

*/

 

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