COMP 1917 Computing 1
Session 2, 2016

Lab Solutions - Week 6

Note: This code should be appropriately commented.

1. printOdd.c
   
   #include 
   #include 
   
   #define MAX 1000
   
   int scanN();
   void printOdd(int n);
   
   int main() {
       int n = scanN();
       //int n = getCharN();
       printOdd(n);
       return 0;
   }
   
   int scanN() {
       int n;
       scanf("%d", &n);
       return n;
   }
   
   
   void printOdd(int n) {
       int i;
       // i = 1 : we want to start printing from 1
       // i <= n : the last thing we possibly want to print is n
       // i += 2 : we're printing odd numbers, which are spaced two apart from each other
       for (i = 1; i <= n; i+=2) {
           printf("%d\n", i);
       }
   }
   

2. tri.c
   // Copied & modified from t1 directory
   // printTRTri offers a different approach to this problem
   //
   // Dong.
   
   #include 
   // Bottom Left Triangle (i.e. right angle at bottom left)
   void printBLTri(int num) {
   
       int i, j;
   
       // Prints the rows (lowerlim;upperlim;inc)
       for (i = 0; i < num; i++) {
   
           int blTri = i + 1;
   
           // Prints the characters of each row
           for (j = 0; j < blTri; j++) {
               printf("*");
           }
           printf("\n");
       }
   }
   // Top Left Triangle (i.e. right angle at top left)
   void printTLTri(int num) {
   
       int i, j;
   
       // Prints the rows (lowerlim;upperlim;inc)
       for (i = 0; i < num; i++) {
   
           int tlTri = num - i;
   
           // Prints the characters of each row
           for (j = 0; j < tlTri; j++) {
               printf("*");
           }
           printf("\n");
       }
   }
   
   // Top Right Triangle (i.e. right angle at top right)
   void printTRTri(int num) {
   
       int i, j;
       for (i = 0; i < num; i++) {
           for (j = 0; j < num; j++) {
               if (j >= i) {
                   printf("*");
               }
               else {
                   printf(" ");
               }
           }
           printf("\n");
       }
   }
   
   // Bottom Right Triangle (i.e. right angle at bottom right)
   void printBRTri(int num) {
   
       int i, j;
   
       // Prints the rows (lowerlim;upperlim;inc)
       for (i = 0; i < num; i++) {
   
           int trTri = num - i;
           //int brTri = i + 1;
   
           // Prints the characters of each row
           for (j = 0; j < trTri - 1; j++) {
               printf(" ");
           }
           for (; j < num; j++) {
               printf("*");
           }
           printf("\n");
       }
   
   }
   
   int main() {
       int num;
       printf("Enter n : ");
       scanf("%d", &num);
       printf(" === Bottom Left Triangle ===\n");
       printBLTri(num);
       printf(" === Bottom Right Triangle ===\n");
       printBRTri(num);
       printf(" === Top Left Triangle ===\n");
       printTLTri(num);
       printf(" === Top Right Triangle ===\n");
       printTRTri(num);
       return 0;
   
   }
   
   

3. pow2.c
   #include 
   
   int isPow2(int n) {
       
       // while n is even, divide by 2
       while (n % 2 == 0) {
           n = n/2;
       }
       if (n == 1) {
           return 1;
       }
       return 0;
   
   }
   
   int main(int argc, char** argv) {
       int n;
       scanf("%d", &n);
       if (isPow2(n)) {
           printf("%d is a power of 2\n", n);
       }
       else {
           printf("%d is not a power of 2\n", n);
       }
       return 0;
   }
   
   

4. freqNum.c
   // README
   // Counts from stdin until EOF is found
   // To test, type in characters and finish with "CTRL-D"
   //
   // Credits to Ka Hei :)
   
   #include 
   
   // Scans user input, counts into the count
   void scanNums(int * count) {
       char c;
       while ((c = getchar()) != EOF) {
           if (c >= '0' && c <= '9') {
               int num = c - '0';
               count[num] = count[num] + 1;
           }
       }
   }
   
   void printFreq(int * count, int n) {
       int i = 0;
       while (i < n) {
           printf("%d %d\n", i, count[i]);
           i++;
       }
   }
   
   int main() {
       int count[10] = {0};
   
       scanNums(count);
   
       printf("\n");
       
       printFreq(count, 10);
       return 0;
   }
   
   

5. average.c
   // Credits to Ka Hei :)
   
   #include 
   
   double average(int len, int a[]) {
       // Returns the average of the array a
       double sum = 0;
       int i = 0;
       while (i < len) {
           sum = sum + a[i];
           i++;
       }
       double avg = sum/len;
       return avg;
   
   }
   
   int main() {
       int a[] = {20, 35, -63, 42, 57};
       int len = 5;
   
       double avg = average(len, a);
       printf("%lf\n", avg);
       return 0;
   }