codepad

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// Increment a very large unsigned number by one
#include <stdio.h>
#include <string.h>

void incrementUnsignedIntByOneAndPrint(const char *s) {
  // Sanity checks like s is not null etc
  int i;
  int len = strlen(s);
  char *inc = malloc(len + 2);
  inc[len] = inc[len+1] = '\0';
  for(i = 0; i <= len; ++i) {
    int d = i;
    // Sanity checks like s[i] is a digis (isnum from ctype)
    while(s[i] == '9') i++;
    if('\0' == s[i]) {
      int offset = 0;
      // increment last digit and add n9s zeros
      if(0 == d) inc[offset++] = '1';
      else ++inc[d-1];
      if(d < i) memset(inc+offset+d, '0', i-d);
    } else {
      // copy all numbers
      if(d < i) memset(inc+d, '9', i-d);
      inc[i] = s[i];
    }
  }
  printf("Input  = %s\n", s);
  printf("Output = %s\n", inc);
  printf("\n");
}

int main() {
  incrementUnsignedIntByOneAndPrint("0");
  incrementUnsignedIntByOneAndPrint("1");
  incrementUnsignedIntByOneAndPrint("9");
  incrementUnsignedIntByOneAndPrint("100");
  incrementUnsignedIntByOneAndPrint("101");
  incrementUnsignedIntByOneAndPrint("109");
  incrementUnsignedIntByOneAndPrint("199");
  incrementUnsignedIntByOneAndPrint("999");
  incrementUnsignedIntByOneAndPrint("9999999999999999999999999999");
  incrementUnsignedIntByOneAndPrint("9999999999999999997999999999");
  incrementUnsignedIntByOneAndPrint("9991999993999999999799999999");
  incrementUnsignedIntByOneAndPrint("1111111111111111111111111111");
  incrementUnsignedIntByOneAndPrint("0000000000000000000000000000");
  return 0;
}

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