Week 2 Laboratory — Sample Solutions

  1. collatz.c 

    // collatz.c: test the 3n+1 conjecture of always eventually reaching 1
#include <stdio.h>

int main(void) {
    int n = 0;

    printf("Enter a positive number:\n");
    scanf("%d", &n);
    if (n > 0) {
	while (n != 1) {
	    if ((n % 2) == 0) {	// n is even
		n = n / 2;
	    } else {
		n = 3*n + 1;
	    }
	    printf("%d\n", n);
	}
    } else {
	printf("Not a positive number.\n");
    }
    return 0;
}

  2. fibonacci.c 

    // fibonacci.c: compute the first 30 Fibonacci numbers
#include <stdio.h>

#define MAX 30

int main(int argc, char *argv[]) {
    int fib[MAX];
    int i;

    fib[0] = 1;
    fib[1] = 1;
    for (i=2; i<MAX; i++) {
	fib[i] = fib[i-1] + fib[i-2];
    }
    for (i=0; i<MAX; i++) {
	printf("fib[%d] = %d\n", i, fib[i]);
    }

    return 0;
}

  3. string.c 

    // string.c: swap 'A' and 'T' in a string
#include <stdio.h>
#include <string.h>

#define MAX_CHARS 128

void convertString(char *);

int main(void) {
    char string[MAX_CHARS];

    printf("Enter a string: ");
    fgets(string, MAX_CHARS, stdin);

    convertString(string);
    printf("%s", string);

    return 0;
}

void convertString(char *string) {
    int i;

    for (i = 0; i < strlen(string); i++) {
	if (string[i] == 'A') {
	    string[i] = 'T';
	} else if (string[i] == 'T') {
	    string[i] = 'A';
	}
    }
}

  4. file.c 

    // file.c: read file and swap all occurrences of 'A' and 'T'
#include <stdio.h>
#include <string.h>

#define MAX_CHARS 128

void convertString(char *);

int main(void) {
    FILE *inputStream;
    char string[MAX_CHARS];

    inputStream = fopen("yeast.dna", "r");
    if (inputStream != NULL) {
	while (fgets(string, MAX_CHARS, inputStream) != NULL) {
	    convertString(string);
	    printf("%s", string);
	}
	fclose(inputStream);
    }
    return 0;
}

void convertString(char *string) {
    int i;

    for (i = 0; i < strlen(string); i++) {
	if (string[i] == 'A') {
	    string[i] = 'T';
	} else if (string[i] == 'T') {
	    string[i] = 'A';
	}
    }
}

  5. floats.c 

    // floats.c: determine the greater of two floating point numbers using pointers
#include <stdio.h>

float *greater(float *, float *);

int main(int argc, char **argv) {
    float x, y;

    printf("Enter a number: ");
    scanf("%f", &x);
    printf("Enter a number: ");
    scanf("%f", &y);

    printf("The greater number is %f\n", *greater(&x, &y));

    return 0;
}

float *greater(float *x, float *y) {
    float *retval;

    if (*x > *y) {
	    retval = x;
    } else {
	retval = y;
    }

    return retval;
}