diff --git a/2.10.txt b/2.10.txt
new file mode 100644
index 0000000..a98cbe7
--- /dev/null
+++ b/2.10.txt
@@ -0,0 +1,23 @@
+  #include <stdio.h>
+
+  int lower(int c);
+
+  int main()
+  {
+      int i;
+
+      char s[] = "DEERTGAD UIOG\0";
+      printf("s = %s\n", s);
+
+      printf("lower s = "); 
+      for (i = 0; s[i] != '\0'; i++)
+          printf("%c", lower(s[i]));
+      printf("\n");
+
+      return 0;
+  }
+
+  /* lower: преобразование прописных c в строчные, только для ASCII */
+  int lower(int c)
+  {
+      return (c >= 'A' && c <='Z') ? c +'a'-'A' : c;
\ No newline at end of file
diff --git a/2.6.txt b/2.6.txt
new file mode 100644
index 0000000..c153809
--- /dev/null
+++ b/2.6.txt
@@ -0,0 +1,38 @@
+#include <stdio.h>
+
+unsigned setbits(unsigned x, int p, int n, unsigned y);
+void printfbit(unsigned n);
+
+int main()
+{
+    printf("76543210\n\n");
+
+    unsigned c1 = 'f';
+    printfbit(c1);
+
+    unsigned c2 = 'z';
+    printfbit(c2);
+
+    printfbit(setbits(c1, 5, 3, c2));
+
+    return 0;
+}
+
+/* setbits: x получает n правых бит из y, начиная с p-й позиции */
+unsigned setbits(unsigned x, int p, int n, unsigned y)
+{
+    return ( (~0 << (p+1)) & x ) | ( ~(~0 << (p+1-n)) & x ) | 
+            (~(~0 << n) & y) << (p+1-n);
+}
+
+void printfbit(unsigned n)
+{
+    for(int i = 7; i >= 0; i--)
+    {
+        if(n & (1 << i))
+            putchar('1');
+        else
+            putchar('0');
+    }
+    putchar('\n');
+}
\ No newline at end of file
diff --git a/2.7.txt b/2.7.txt
new file mode 100644
index 0000000..d2d92d7
--- /dev/null
+++ b/2.7.txt
@@ -0,0 +1,34 @@
+#include <stdio.h>
+
+unsigned invert(unsigned x, int p, int n);
+void printfbit(unsigned n);
+
+int main()
+{
+    printf("76543210\n\n");
+
+    unsigned c = 'f';
+    printfbit(c);
+
+    printfbit(invert(c, 5, 3));
+
+    return 0;
+}
+
+/* invert: инвертирует n бит из x, начиная с p-й позиции */
+unsigned invert(unsigned x, int p, int n)
+{
+    return x ^ (~(~0 << n) << (p+1-n));
+}
+
+void printfbit(unsigned n)
+{
+    for(int i = 7; i >= 0; i--)
+    {
+        if(n & (1 << i))
+            putchar('1');
+        else
+            putchar('0');
+    }
+    putchar('\n');
+}
\ No newline at end of file
diff --git a/3.1.txt b/3.1.txt
new file mode 100644
index 0000000..3795af6
--- /dev/null
+++ b/3.1.txt
@@ -0,0 +1,19 @@
+ /* binsearch: найти х в v[0] <= v[1] <= … <= v[n-1] */
+int main(int x, int v[], int n)
+{
+    int low, high, mid;
+    low = 0;
+    high = n - 1 ;
+    while (low <= high && x != v[mid]) {
+        mid = (low + high) / 2;
+        if (x < v[mid])
+            high = mid - 1;
+        else
+            low = mid + 1;
+        mid = (low + high) / 2;  \
+    }
+    if ( x == v[mid])
+        return mid;
+    else
+        return -1; /* совпадения нет */
+}
\ No newline at end of file
diff --git a/3.2.txt b/3.2.txt
new file mode 100644
index 0000000..a3614a8
--- /dev/null
+++ b/3.2.txt
@@ -0,0 +1,65 @@
+ #include <stdio.h>
+
+  #define MAXLEN 30
+
+  void escape(char s[], char t[]);
+  void unescape(char s[], char t[]);
+
+  int main()
+  {
+      char input[MAXLEN] = "bla\tbla\nbla\n";
+      char output[MAXLEN];
+
+      printf("Original   = %s\n", input);
+      escape(output, input);
+      printf("Escaped    = %s\n", output);
+      unescape(input, output);
+      printf("Unescaped  = %s\n", input);
+      printf("The End\n");
+
+      return 0;
+  }
+
+  void escape(char s[], char t[])
+  {
+      int i, j;
+
+      for (i = 0, j = 0; s[i]; i++, j++)
+          switch (t[i]) {
+          case '\t':
+              s[j++] = ' ';
+              s[j] = 't';
+              break;
+          case '\n':
+              s[j++] = ' ';
+              s[j] = 'n';
+              break;
+          default:
+              s[j] = t[i];
+              break;
+          }
+      s[j] = t[i];  // \0  !
+  }
+
+  void unescape(char s[], char t[])
+  {
+      int i, j;
+
+      for (i = 0, j = 0; s[i]; i++, j++)
+          switch (t[i]) {
+          case ' ':
+              switch (t[++i]) {
+              case 't':
+                  s[j] = '\t';
+                  break;
+              case 'n':
+                  s[j] = '\n';
+                  break;
+              }
+              break;
+          default:
+              s[j] = t[i];
+              break;
+          }
+      s[j] = t[i];
+  }
\ No newline at end of file
diff --git a/3.4.txt b/3.4.txt
new file mode 100644
index 0000000..d6e2d5a
--- /dev/null
+++ b/3.4.txt
@@ -0,0 +1,46 @@
+#include <stdio.h>
+  #include <string.h>
+  #include <limits.h>
+
+  void itoa(int n, char s[]);
+  void reverse(char s[]);
+
+  int main(void) {
+      char buffer[20];
+      int i = 35;
+
+      printf("Number: %d\n", i);
+      itoa(i, buffer); 
+      printf("Buffer : %s\n", buffer);
+
+      printf("INT_MIN: %d\n", INT_MIN);
+      itoa(INT_MIN, buffer);
+      printf("Buffer : %s\n", buffer);
+
+      return 0;
+  }
+
+/* itoa: преобразование n в строку s */
+  void itoa(int n, char s[]) {
+      int i, sign;
+      sign = n; /* сохраняем знак */
+
+      i = 0;
+      do { /* генерируем цифры в обратном порядке */
+          s[i++] = abs(n % 10) + '0'; /* следующая цифра */
+      } while ( n /= 10 );            /* исключить ее */
+      if (sign < 0)
+          s[i++] = '-';
+
+      s[i] = '\0';
+      reverse(s);
+  }
+
+  void reverse(char s[]) {
+      int c, i, j;
+      for ( i = 0, j = strlen(s)-1; i < j; i++, j--) {
+          c = s[i];
+          s[i] = s[j];
+          s[j] = c;
+      }
+  }
\ No newline at end of file
diff --git a/3.5.txt b/3.5.txt
new file mode 100644
index 0000000..4bdb71e
--- /dev/null
+++ b/3.5.txt
@@ -0,0 +1,38 @@
+#include <stdio.h>
+#include <string.h>
+#include <math.h>
+
+
+int convert_base(char *p, int b, int s);
+
+int main() {
+    char p[] = "111";
+    int b = 10;
+    int s = 8;
+
+    int result = convert_base(p, b, s);
+    printf("Converted number: %d\n", result);
+
+    return 0;
+}
+// Функция для конвертации числа из одного основания в другое
+int convert_base(char *p, int b, int s) {
+    int decimal = 0;
+    int len = strlen(p);
+
+    // Преобразование числа в десятичную систему счисления
+    for (int i = 0; i < len; i++) {
+        decimal += (p[i] - '0') * pow(b, len - i - 1);
+    }
+
+    // Преобразование десятичного числа в нужное основание
+    int result = 0;
+    int index = 0;
+    while (decimal > 0) {
+        result += (decimal % s) * pow(10, index);
+        decimal /= s;
+        index++;
+    }
+
+    return result;
+}
\ No newline at end of file