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  1. #include <stdio.h>
  2. #include <string.h>
  3.  
  4. // Max size for data and polynomial
  5. #define MAX 100
  6.  
  7. char t[MAX], cs[MAX], g[] = "1011"; 
  8. int a, e, c;
  9.  
  10. // Function to perform XOR operation
  11. void xor_func() {
  12.     int N = strlen(g);
  13.     for (c = 1; c < N; c++) {
  14.         cs[c] = ((cs[c] == g[c]) ? '0' : '1');
  15.     }
  16. }
  17.  
  18. // Function to calculate CRC/Remainder
  19. void crc_calc() {
  20.     int N = strlen(g);
  21.     // Initialize cs with the first N bits of t
  22.     for (e = 0; e < N; e++) {
  23.         cs[e] = t[e];
  24.     }
  25.  
  26.     int next_bit = N;
  27.     do {
  28.         if (cs[0] == '1') {
  29.             xor_func();
  30.         }
  31.  
  32.         // Shift bits left by 1
  33.         for (c = 0; c < N - 1; c++) {
  34.             cs[c] = cs[c + 1];
  35.         }
  36.         // Pull the next bit from the data
  37.         cs[c] = t[next_bit++];
  38.  
  39.     } while (next_bit <= a + N - 1);
  40. }
  41.  
  42. int main() {
  43.     // Clear arrays
  44.     memset(t, 0, MAX);
  45.     memset(cs, 0, MAX);
  46.  
  47.     printf("Enter data bits: ");
  48.     scanf("%s", t);
  49.  
  50.     a = strlen(t); // Original data length
  51.     int N = strlen(g); // Polynomial length
  52.  
  53.     printf("\nGenerating polynomial: %s", g);
  54.  
  55.     // Append N-1 zeros to the data (Padding)
  56.     for (e = a; e < a + N - 1; e++) {
  57.         t[e] = '0';
  58.     }
  59.     t[e] = '\0';
  60.  
  61.     printf("\nData after padding: %s", t);
  62.  
  63.     crc_calc(); // Calculate Checksum
  64.  
  65.     printf("\nCalculated Checksum: %s", cs);
  66.  
  67.     // Replace the padding bits with the actual checksum bits
  68.     for (e = a; e < a + N - 1; e++) {
  69.         t[e] = cs[e - a];
  70.     }
  71.  
  72.     printf("\nFinal Codeword to be sent: %s", t);
  73.     printf("\n---------------------------------------");
  74.  
  75.     // Error simulation
  76.     printf("\nTest error detection? (1 for Yes, 0 for No): ");
  77.     int choice;
  78.     scanf("%d", &choice);
  79.  
  80.     if (choice == 1) {
  81.         printf("Enter bit position to flip (1 to %d): ", (int)strlen(t));
  82.         int pos;
  83.         scanf("%d", &pos);
  84.         if(pos > 0 && pos <= (int)strlen(t)) {
  85.             t[pos - 1] = (t[pos - 1] == '0') ? '1' : '0';
  86.             printf("Data with error: %s", t);
  87.         }
  88.     }
  89.  
  90.     crc_calc(); // Recalculate to verify
  91.  
  92.     // Check if remainder (cs) is all zeros
  93.     int error_found = 0;
  94.     for (e = 0; e < N - 1; e++) {
  95.         if (cs[e] == '1') {
  96.             error_found = 1;
  97.             break;
  98.         }
  99.     }
  100.  
  101.     printf("\n---------------------------------------");
  102.     if (error_found) {
  103.         printf("\nRESULT: Error detected (Remainder is not 0)");
  104.     } else {
  105.         printf("\nRESULT: No error detected (Data is clean)");
  106.     }
  107.     printf("\n---------------------------------------\n");
  108.  
  109.     return 0;
  110. }
Success #stdin #stdout 0s 5304KB
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stdin
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45
stdout
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Enter data bits: 
Generating polynomial: 1011
Data after padding: 45000
Calculated Checksum: 000
Final Codeword to be sent: 45000
---------------------------------------
Test error detection? (1 for Yes, 0 for No): 
---------------------------------------
RESULT: No error detected (Data is clean)
---------------------------------------
https://ideone.com/QyZuuu
language:
C++14 (gcc 8.3)
created:
6 hours ago
visibility:
public

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