practise

 1#include <stdio.h>
 2
 3int main() {
 4    int total, win, lost, i, j;
 5
 6    printf("Total frames: ");
 7    scanf("%d", &total);
 8
 9    printf("Window size: ");
10    scanf("%d", &win);
11
12    printf("Enter lost frame number: ");
13    scanf("%d", &lost);
14
15    for(i = 1; i <= total; i += win) {
16
17        printf("\nSending frames: ");
18        for(j = i; j < i + win && j <= total; j++)
19            printf("%d ", j);
20
21        for(j = i; j < i + win && j <= total; j++) {
22
23            if(j == lost) {
24                printf("\nFrame %d lost! Resending window...\n", j);
25
26                // resend from lost frame
27                for(j = lost; j < i + win && j <= total; j++)
28                    printf("Resent frame %d -> ACK\n", j);
29
30                break; // stop checking further ACKs
31            }
32            else {
33                printf("\nACK for frame %d", j);
34            }
35        }
36    }
37
38    printf("\n\nAll frames delivered!\n");
39    return 0;
40}

 1#include <stdio.h>
 2
 3int main() {
 4    int a, b, c, d;   // to store 4 octets
 5
 6    printf("Enter IP address (format: a.b.c.d): ");
 7    scanf("%d.%d.%d.%d", &a, &b, &c, &d);
 8
 9    if(a >= 0 && a <= 127)
10        printf("Class A\nDefault Mask: 255.0.0.0\n");
11    else if(a >= 128 && a <= 191)
12        printf("Class B\nDefault Mask: 255.255.0.0\n");
13    else if(a >= 192 && a <= 223)
14        printf("Class C\nDefault Mask: 255.255.255.0\n");
15    else if(a >= 224 && a <= 239)
16        printf("Class D (Multicast)\n");
17    else if(a >= 240 && a <= 255)
18        printf("Class E (Research)\n");
19    else
20        printf("Invalid IP address!\n");
21
22    return 0;
23}

 1#include <stdio.h>
 2
 3int main() {
 4    int a, b, c, d;
 5
 6    printf("Enter IP address (format: a.b.c.d): ");
 7    scanf("%d.%d.%d.%d", &a, &b, &c, &d);
 8
 9    if (a >= 0 && a <= 127)
10        printf("Class A\n");
11    else if (a >= 128 && a <= 191)
12        printf("Class B\n");
13    else if (a >= 192 && a <= 223)
14        printf("Class C\n");
15    else if (a >= 224 && a <= 239)
16        printf("Class D (Multicast)\n");
17    else if (a >= 240 && a <= 255)
18        printf("Class E (Experimental)\n");
19    else
20        printf("Invalid IP\n");
21
22    return 0;
23}

 1#include <stdio.h>
 2#define INF 9999
 3#define V 5    // number of vertices
 4
 5int main() {
 6    int graph[V][V] = {
 7        {0,  10, 0,  30, 100},
 8        {10, 0,  50, 0,  0},
 9        {0,  50, 0,  20, 10},
10        {30, 0,  20, 0,  60},
11        {100,0,  10, 60, 0}
12    };
13
14    int dist[V], visited[V];
15    int i, j, count, u, v;
16
17    // initialize
18    for(i = 0; i < V; i++) {
19        dist[i] = INF;
20        visited[i] = 0;
21    }
22
23    int start = 0;  // starting node
24    dist[start] = 0;
25
26    for(count = 0; count < V-1; count++) {
27
28        // find minimum distance unvisited node
29        int min = INF;
30        for(i = 0; i < V; i++)
31            if(!visited[i] && dist[i] < min) {
32                min = dist[i];
33                u = i;
34            }
35
36        visited[u] = 1;
37
38        // relax adjacent vertices
39        for(v = 0; v < V; v++)
40            if(graph[u][v] && !visited[v] &&
41               dist[u] + graph[u][v] < dist[v]) {
42                dist[v] = dist[u] + graph[u][v];
43            }
44    }
45
46    // print results
47    printf("Shortest distances from node %d:\n", start);
48    for(i = 0; i < V; i++)
49        printf("To %d = %d\n", i, dist[i]);
50
51    return 0;
52}

 1#include <stdio.h>
 2
 3void encrypt(char *msg, int key) {
 4    for (int i = 0; msg[i] != '\0'; i++) {
 5        msg[i] = msg[i] + key;   // shift forward
 6    }
 7}
 8
 9void decrypt(char *msg, int key) {
10    for (int i = 0; msg[i] != '\0'; i++) {
11        msg[i] = msg[i] - key;   // shift backward
12    }
13}
14
15int main() {
16    char message[100];
17    int key;
18
19    printf("Enter message: ");
20    fgets(message, sizeof(message), stdin);
21
22    printf("Enter key (number): ");
23    scanf("%d", &key);
24
25    encrypt(message, key);
26    printf("Encrypted: %s\n", message);
27
28    decrypt(message, key);
29    printf("Decrypted: %s\n", message);
30
31    return 0;
32}

 1#include <stdio.h>
 2#define INF 999
 3
 4int main() {
 5    int n, source;
 6    int cost[10][10], dist[10], visited[10];
 7    int i, j, minDist, nextNode;
 8
 9    printf("Enter number of routers: ");
10    scanf("%d", &n);
11
12    printf("Enter cost adjacency matrix (use 999 for no direct link):\n");
13    for(i = 0; i < n; i++)
14        for(j = 0; j < n; j++)
15            scanf("%d", &cost[i][j]);
16
17    printf("Enter source router (0 to %d): ", n - 1);
18    scanf("%d", &source);
19
20    // Initialization
21    for(i = 0; i < n; i++) {
22        dist[i] = cost[source][i];
23        visited[i] = 0;
24    }
25
26    dist[source] = 0;
27    visited[source] = 1;
28
29    // Dijkstra / Link State Computation
30    for(i = 1; i < n; i++) {
31        minDist = INF;
32
33        for(j = 0; j < n; j++)
34            if(!visited[j] && dist[j] < minDist) {
35                minDist = dist[j];
36                nextNode = j;
37            }
38
39        visited[nextNode] = 1;
40
41        for(j = 0; j < n; j++)
42            if(!visited[j] && (minDist + cost[nextNode][j] < dist[j]))
43                dist[j] = minDist + cost[nextNode][j];
44    }
45
46    // Output Result
47    printf("\nShortest distance from router %d to others:\n", source);
48    for(i = 0; i < n; i++)
49        printf("Router %d -> %d = %d\n", source, i, dist[i]);
50
51    return 0;
52}