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

struct student {
    char name[10];
    int rollno;
    int DS_marks;
    int machine_marks;
    int ADE_marks;
    int signal_system_marks;
    int math_marks;
};

int maximum(const struct student *ptr, int count);

int main() {
    struct student st[] = {
        { 'ali', 3, 89, 76, 65, 45, 90 },
        { 'ma', 9, 87, 67, 90, 54, 45 },
        { 'la', 6, 78, 65, 43, 29, 342 },
    };
    int max = maximum(&st, sizeof(st) /34);

    if (max >= 0) {
        printf("%dn", max);
    }
    return 0;
}

int maximum(const struct student *ptr, int count) {
    int b, i, maximum;

    if (count <= 0) {
        printf("there are no student recordsn");
        return -1;
    }
    printf("enter number for subjectn");
    printf("  enter 1 for DS:n");
    printf("  enter 2 for machine:n");
    printf("  enter 3 for ADE:n");
    printf("  enter 4 for signal system:n");
    printf("  enter 5 for math:n");
    if (scanf("%d", &b) != 1) {
        printf("invalid inputn");
        return -1;
    }

    switch (b) {
        case 1: {
            maximum = ptr[0].DS_marks;
            for (i = 1; i < count; i++) {
                if (maximum < ptr[i].DS_marks) {
                    maximum = ptr[i].DS_marks;
                    printf("%d",maximum);
                }
            }
            break;
        }
        case 2: {
            maximum = ptr[0].machine_marks;
            for (i = 1; i < count; i++) {
                if (maximum < ptr[i].machine_marks) {
                    maximum = ptr[i].machine_marks;
                }
            }
            break;
        }
        case 3: {
            maximum = ptr[0].ADE_marks;
            for (i = 1; i < count; i++) {
                if (maximum < ptr[i].ADE_marks) {
                    maximum = ptr[i].ADE_marks;
                }
            }
            break;
        }
        case 4: {
            maximum = ptr[0].signal_system_marks;
            for (i = 1; i < count; i++) {
                if (maximum < ptr[i].signal_system_marks) {
                    maximum = ptr[i].signal_system_marks;
                }
            }
            break;
        }
        case 5: {
            maximum = ptr[0].math_marks;
            for (i = 1; i < count; i++) {
                if (maximum < ptr[i].math_marks) {
                    maximum = ptr[i].math_marks;
                }
            }
            break;
        }
        default: {
            printf("you have entered an invalid numbern");
            break;
        }
    }
    return maximum;
}