Arrays

1. Which of the following array declarations are valid.

1. int [] arr = { 1, 2, 3, 4 };

Ans: Invalid. [] should be placed after arr.

 

2. int arr[] = { ‘1’, ‘2’, ‘3’, ‘4’ };

Ans: Valid. char literals are encoded as int. Array size is determined from number of values in initialization.

 

3. float price = { 2.2, 3.4, 5.5 };

Ans: Invalid. price is not declared as an array – missing [].

 

4. double perimeter[7] = { 0 };

Ans: Valid. Array of 7 double values, all initialized to 0.

 

5. char keyword[5] = { ‘A’ };

Ans: Valid. Array of 5 char values, all initialized to ‘A’.

 

 

2. Write a program to find highest value in an array of 10 integers.

#include<stdio.h>

int main (int argc, char * argv[])  {
    int arr [] = { 1, 2, 3, 4, 5, 6, 7, 10, 8, 9 };

    /* If we initialize max to 0, program will fail if
     * all elements of array were negative. */
    int max = arr[0];

    for(int i=1; i<10; i++) {
        if(arr[i] > max) {
            max = arr[i];
        }
    }
    printf("Max value in array is %d\n", max);
    return 0;
}

 

 

3. Write a program to compute the average of 10 float numbers in an array.

#include<stdio.h>

int main (int argc, char * argv[])  {
    float arr [] = { 1.2, 2.1, 3.4, 9.4, 10.5, 6.6, 0.7, 10, 8.8, 1.9 };
    float average = 0.0;

    for(int i=0; i<10; i++) {
        average += arr[i];
    }
    average /= 10;
    printf("Average of array is %f\n", average);
    return 0;
}

 

 

4. What will be the output of following program.

#include <stdio.h>

int main (int argc, char * argv[]) {
    int arr[] = { 0,1,2,3,4,5,6,7,8,9 };
    int i=0;
    int num_elements = 10;
    for(i=9; i>=0; i--) {
        arr[i] = arr[num_elements - i - 1] + arr[i];
    }
    for(i=0; i<num_elements; i++) {
        printf("arr[%d] = %d\n", i, arr[i]);
    }
    return 0;
}

 

Ans:

arr[0] = 9

arr[1] = 10

arr[2] = 11

arr[3] = 12

arr[4] = 13

arr[5] = 9

arr[6] = 9

arr[7] = 9

arr[8] = 9

arr[9] = 9

 

 

5. Enhance the above program to add two functions find_max and find_min to find the highest and lowest scores respectively.

01: #include <stdio.h>

02: float compute_average(int marks[], int size);

03: int main (int argc, char * argv[]) {
04:     int marks[50] = { 0 };
05:     int i=0;
06:     float average = 0.0;

07:     do {
08:         printf ("Enter marks for student %d", i+1);
09:         scanf("%d",&marks[i]);
10:         i++;
11:     }while(i<50);

12:     average = compute_average(marks, 50);
13:     printf("Average score is %f\n", average);
14:     return 0;
15: }

16: float compute_average(int marks[], int size) {
17:     int i=0, sum=0;
18:     for(i=0; i<size; i++) {
19:         sum = sum + marks[i];
20:     }
21:     return ((1.0*sum)/size);
22: }

int find_max(int marks[], int size) {
    int max = marks[0];
    for(int i=1; i<size; i++) {
        if(marks[i] > max) {
            max = marks[i];
        }
    }
    return max;
}

int find_min(int marks[], int size){
    int min = marks[0];
    for(int i=1; i<size; i++) {
        if(marks[i] < min) {
            min = marks[i];
        }
    }
    return min;
}

 

 

6. Write a program to search a value in an array of integers.

int find_val(int arr[], int size, int val){
    for(int i=0; i<size; i++) {
        if(arr[i] == val) {
            return i;
        }
    }
    return -1;
}

 

 

7. Write a program that inputs two arrays of 10 integers each and saves sum of corresponding elements of these arrays in a third array and prints them.

#include <stdio.h>
#define ARRAY_SIZE 10

void read_arr(int [], int);
void add_arr(int [], int [], int [], int);

int main (int argc, char * argv[]) {
    int arr1[ARRAY_SIZE] = { 0 };
    int arr2[ARRAY_SIZE] = { 0 };
    int result[ARRAY_SIZE] = { 0 };

    read_arr(arr1, ARRAY_SIZE);
    read_arr(arr2, ARRAY_SIZE);
    add_arr(arr1, arr2, result, ARRAY_SIZE);
    for(int i=0; i<ARRAY_SIZE; i++) {
        printf("%d + %d = %d\n", arr1[i], arr2[i], result[i]);
    }
    return 0;
}

void read_arr(int arr[], int size) {
    for(int i=0; i<size; i++) {
        printf("Enter element %d ", i+1);
        scanf("%d", &arr[i]);
    }
}

void add_arr(int arr1[], int arr2[], int result[], int size) {
    for(int i=0; i<size; i++) {
        result[i] = arr1[i] + arr2[i];
    }
}

 

 

8. Trace control flow of above example.

01: #include<stdio.h>
02: int main (int argc, char * argv[])  {
03:     int marks[5][3] = { 0 };
04:     int student=0, subject=0, sum=0;

05:     for(student=0; student<5; student++) {
06:         for(subject=0; subject<3; subject++) {
07:             printf("Enter marks for student %d subject %d: ",student,subject);
08:             scanf("%d",&marks[student][subject]);
09:         }
10:     }

11:     for(student=0; student<5; student++) {
12:         sum = 0;
13:         for(subject=0; subject<3; subject++) {
14:             sum = sum + marks[student][subject];
15:         }
16:         printf("Student %d scored total %d\n", student, sum);
17:     }

18:     return 0;
19: }

 

1. After initialization, control reaches line 05.
2. Control expression 0<5 is true. Control enters for loop, line 06.
3. Another for loop. Control expression 0<3 evaluates to true. Control enters nested loop, line 07.
4. Message Enter marks for student 0 subject 0: is printed to the console. Control advances to line 08 and input is read.
5. End of nested loop is reached. Tail statement is executed. Value of subject is incremented to 1. Control jumps to line 06.
6. Control expression 1<3 evaluates to true. Control enters nested loop, line 07.
7. Message Enter marks for student 0 subject 1: is printed to the console. Control advances to line 08 and input is read.
8. End of nested loop is reached. Tail statement is executed. Value of subject is incremented to 2. Control jumps to line 06.
9. Control expression 2<3 evaluates to true. Control enters nested loop, line 07.
10. Message Enter marks for student 0 subject 2: is printed to the console. Control advances to line 08 and input is read.
11. End of nested loop is reached. Tail statement is executed. Value of subject is incremented to 3. Control jumps to line 06.
12. Control expression 3<3 evaluates to false. Control jumps out of nested loop, line 10.
13. End of outer loop is reached. Tail statement is executed. Value of student is incremented to 1. Control jumps to line 05.
14. Steps 2-13 are repeated for all values student from 1 to 4.
15. When value of student is incremented to 5, control jumps out of outer loop, line 11.
16. Value of student is set to 0.
17. Control expression 0<5 is true. Control enters for loop, line 12.
18. Value of sum is set to 0. Note that since we need to compute total for each student, we set sum to 0 before we start adding marks for that student.
19. Control advances to line 13. Value of subject is set to 0.
20. Control expression 0<3 is true. Control enters for loop, line 14.
21. Value of marks[0][0] is added to sum.
22. End of nested loop is reached. Control statement is executed and value of subject is incremented to 1.
23. Control expression 1<3 is true. Control etners for loop, line 14.
24. Value of marks[0][1] is added to sum.
25. End of nested loop is reached. Control statement is executed and value of subject is incremented to 2.
26. Control expression 2<3 is true. Control etners for loop, line 14.
27. Value of marks[0][2] is added to sum.
28. End of nested loop is reached. Control statement is executed and value of subject is incremented to 3.
29. Control expression 3<3 is false. Control jumps out of nested for loop, line 16.
30. Message student 0 scored total is printed with value of sum.
31. Control advances to line 17, end of outer for loop.
32. Tail statement is executed. Value of student is incremented to 1.
33. Steps 20-31 are executed for all values of student from 1-4.
34. When value of student is incremented to 5, control jumps out of outer for loop, line 18.
35. Program terminates.

 

9. Enhance the above example to print average marks of each student in addition to total marks.

#include<stdio.h>

int main (int argc, char * argv[])  {
    int marks[5][3] = { 0 };
    int student=0, subject=0, sum=0;

    for(student=0; student<5; student++) {
        for(subject=0; subject<3; subject++) {
            printf("Enter marks for student %d subject %d: ",student, subject);
            scanf("%d",&marks[student][subject]);
        }
    }


    for(student=0; student<5; student++) {
        sum = 0;
        for(subject=0; subject<3; subject++) {
            sum = sum + marks[student][subject];
        }
        printf("Student %d scored total %d and average %f\n", student, sum, sum/3.0);
    }
    return 0;
}

 

10. Enhance the program further to print class average marks in each subject.

#include<stdio.h>

int main (int argc, char * argv[])  {
    int marks[5][3] = { 0 };
    int student=0, subject=0, sum=0;

    for(student=0; student<5; student++) {
        for(subject=0; subject<3; subject++) {
            printf("Enter marks for student %d subject %d: ",student,subject);
            scanf("%d",&marks[student][subject]);
        }
    }

    for(student=0; student<5; student++) {
        sum = 0;
        for(subject=0; subject<3; subject++) {
            sum = sum + marks[student][subject];
        }
        printf("Student %d scored total %d and average %f\n", student, sum, sum/3.0);
    }

    for(subject=0; subject<3; subject++) {
        sum = 0;
        for(student=0; student<5; student++) {
            sum = sum + marks[student][subject];
        }
        printf("Average score for subject %d is %f\n", subject, sum/5.0);
    }

    return 0;
}