COMP 1917 Computing 1
Session 2, 2015

Lab Solutions - Week 6

Note: This code should be appropriately commented.

1. Write a program which scans an integer n from standard input and then prints all the odd numbers between 1 and n.

   #include <stdlib.h>
   #include <stdio.h>
   
   int main (int argc, char * argv[]) {
       
       //get number
       int n;
       scanf("%d",&n);
       
       int i = 1;//set counter to first odd number
       
       //loop until i is greater than n
       while (i <= n) {
           printf("%d\n",i);
           i += 2;//i = i + 2 to get next odd number
       }
   
       return EXIT_SUCCESS;
   }
   

2. Write a program which scans an integer n from standard input and then prints a triangle of size n using the star character '*'.

   #include <stdlib.h>
   #include <stdio.h>
   
   int main (int argc, char * argv[]) {
       
       //get number
       int num;
       scanf ("%d",&num);
       
       //set counters --> both are used decreasing!
       int line = num;
       int star;
       
       while (line > 0) {
           star = line;//number of stars per line is current line counter
           
           //print all the stars
           while (star > 0) {
               printf("*");
               star--;
           }
           
           printf("\n");
           line--;
       }
       
       return EXIT_SUCCESS;
   }
   

3. Write a function power_of_two(int k) which takes an ineger k and returns 1 if k is a power of 2, and returns 0 otherwise.

   #define TRUE 1
   #define FALSE 0
   
   int power_of_two(int k) {
       
       //continually divide k by two until you reach an odd number
       while (k % 2 == 0) {//while k is still divisbile by two
           k /= 2; //k = k / 2
       }
       
       int isPow = FALSE;//assume not true
       
       //mathematically, if k ends up as 1, k is a power of 2
       //as it is always reached when you continually divide
       //powers of two by two.
       if (k == 1) {
           isPow = TRUE;
       }
       
       return isPow;
   }
   

4. Write a function average(int n, int a[]) which takes an integer n together with an array a[] of n integers, and prints the average of the n items in this array, to two decimal places.

   void average(int n, int a[]) {
       
       float sum = 0;//use a flaot so that later when you divide
       int i = 0;    //you don't just get the integer part of the answer
       
       //adds the value of every element of the array to sum
       while (i < n) {
           sum += a[i];//sum = sum + a[i]
           
           i++;
       }
       
       float avg = n / sum;//get the average
       
       printf("avg = %.2f\n", avg);
   
   }
   

5. Write a program which continually scans characters from standard input until EOF is reached, then prints the number of times that each of the digits '0' to '9' has occurred in the input.

   #include <stdlib.h>
   #include <stdio.h>
   
   #define FALSE 0
   #define TRUE 1
   #define NUM_DIGITS 10
   
   int isDigit(char c);
   int digitVal(char c);
   
   int main (int argc, char * argv[]) {
       
       int count[NUM_DIGITS] = {}; //set up empty array to count each digit
       int val;
       
       char c = getchar();//getchar() loop to read each character
       while (c != EOF) {
           
           //if it's a digit increment its count by one
           if (isDigit(c)) {
               val = digitVal(c);//convert char to int value
               count[val]++;
           }
           
           c = getchar();
       }
       
       //loop through each digit and print the count
       int i = 0;
       while (i < NUM_DIGITS) {
           printf("%d %d\n", i, count[i]);
           i++;
       }
   
       return EXIT_SUCCESS;
   }
   
   int isDigit(char c) {
       //this function takes in a character
       //and returns FALSE or TRUE
       //depending on whether the char is a digit
       
       int flag = FALSE;//assume not a digit
       
       if (c >= '0' && c <= '9') {//if it is in the digit range of characters
           flag = TRUE;
       }
       
       return flag;
   }
   
   int digitVal(char c) {
       //this function takes in a character and
       //returns the integer value represented
       //note: character passed in must be a digit
       
       //subtract ascii value of '0' from c's ascii value to get the value of the number
       int val = c - '0';
       
       return val;
   }