11.1 Lab3

Introduction to Computer Science

Laboratory 3 November 1, 2024

Exercises

Write a C program that asks the user for an integer value n and then prints the multiplication table for n.

Example: For n = 3, the output should be:

3 * 0 = 0 3 * 1 = 3 ... 3 * 10 = 30

#include <stdio.h>
int main() {
    int n, t=0;
    scanf("%d",&n);
    while (t<11) {
        printf("%d * %d =%d\n", n, t, n*t);
        t++;
    }
    return 0;
}

Write a C program that asks the user for an integer n and then prints all of the digits of n. Utilize a do-while loop.

Hint: Use the modulo operation % to get the last digit of a number.

#include <stdio.h>
#include <math.h>

int main() {
    // number needs user to input, digit is output digit at one time, times defines both the digits of number and how many times do the loop run //
    int number, digit, times = 1;
    scanf("%d", &number);

    // calculate the digits of a number, q is 计数器 //
    int q = number;
    while (q >= 10) {
        q = q / 10;
        times++;
    }

    // calculate the seperate digit //
    do {
        // because (int)pow(10,0)==0, thus we need to use if to fix this problem //
        if ((int)pow(10, times - 1) == 0) {
            // this only happen when we have 1 digit number //
            digit = number % (int)(pow(10, times));
        } else {
            // for example, (1234%1000-1234%100)/100=2 //
            digit = (number % (int)(pow(10, times)) - (number % (int)(pow(10, times - 1)))) / (int)(pow(10, times - 1));
        }
        printf("%d ", digit);
        times = times - 1;
    } while (times != 0);

    return 0;
}

Write a C program that asks the user for a number n and then prints the first n even numbers.

#include <stdio.h>

int main() {
    int n, number=0;
    scanf("%d", &n);
    while (n!=0) {
        printf("%d", number);
        number=number+2;
        n--;
        }
    return 0;
}

Write a C program that asks the user for an integer n and then prints the factorial of n.

#include <stdio.h>

int main() {
    int n, number=1;
    scanf("%d", &n);
    while (n!=0) {
        number=number*n;
        n--;
        }
    printf("%d", number);
    return 0;
}

Write a C program that uses the rand function to generate a random number r (from 0 to 100). Then, the program should ask the user to enter numbers until they guess r. For each attempt, the program should indicate if the attempt is greater or lower than r.

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

int main() {
    int n, random;
    srand(time(0));
    random=rand()%100;
    do {
        printf("Please enter a number from 0 to 100: ");
        scanf("%d", &n);
        if (n>random) 
            printf("Too big!\n");
        else if (n<random)
            printf("Too small!\n");
        else 
            printf("Yes, you are right!\n");
    } while (n != random);

    return 0;
}

A more advanced version

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

int main() {
    int n, random, max = 100, min = 0;
    srand(time(0));
    random = rand()%100;
    do {
        printf("Please enter a number from %d to %d: ", min, max);
        scanf("%d", &n);
        if (n > random) {
            max = n;
            printf("Too big! Try again!\n");
        }
        else if (n < random) {
            min = n;
            printf("Too small! Try again!\n");
        }
        else 
            printf("Yes, you are right!\n");

    } while (n != random);

    return 0;
}

Modify the last C program to limit the number of guessing attempts to 5.

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

int main() {
    int n, random, max = 100, min = 0, times=5;
    srand(time(0));
    random = rand()%100;
    do {
        printf("%d attempts, please enter a number from %d to %d: ", times, min, max);
        scanf("%d", &n);
        if (n > random) {
            max = n;
            printf("Too big! Try again!\n");
        }
        else if (n < random) {
            min = n;
            printf("Too small! Try again!\n");
        }
        else 
            printf("Yes, you are right!\n");
        times--;
    } while (n != random && times!=0 );
    printf("Game over!\n");
    return 0;
}

Write a C program that asks the user for an integer number n and prints the nth number of the Fibonacci sequence.

Example: For n = 6, the output should be: 0, 1, 1, 2, 3, 5, 8

#include <stdio.h>

int main() {
    int n, sum_old=0, sum_new=1, x;
    printf("Please enter a number to generate the nth number of the Fibonacci sequence:");
    scanf("%d", &n);
    printf("0 1 ");
    while ((n-1) != 0) {
        //memorize sum_new because it will change but we need its later//
        x=sum_new;
        sum_new=sum_new+sum_old;
        //give it back//
        sum_old=x;
        n--;
        printf("%d ", sum_new);
    }
    return 0;
}

How to determine a prime number or composite number?

#include <stdio.h>

int main() {
    int n, divisor=2;
    printf("Please enter a number and I will tell whether it is a prime or not: ");
    scanf("%d", &n);
    while (divisor < n) {
        if (n % divisor != 0) {
            divisor++;
        }
        else {
            printf("%d is a coposite number!", n);
            return 0;
        }
    }
    printf("%d is a prime number!", n);
    return 0;
}

How to calculate the greatest common divisor?

#include <stdio.h>

int main() {
    int x, y, gcd = 1, divisor = 2, max;
    printf("Please enter two numbers and I will calculate the greatest common divisor:");
    scanf("%d %d", &x, &y);
    // determine what the largest divisor should be
    if (x <= y) {
        max = x;
    }
    else {
        max = y;
    }
    while (divisor <= max) {
        if ((x % divisor) != 0 || (y % divisor) != 0) {
            divisor++;
        }
        else {
            gcd = divisor;
            divisor++;
        }
    }
    printf("The greatest common divisor between %d and %d is %d ", x, y, gcd);
}

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