diff --git "a/Turtle-hwan/chapter01/chapter01_wsl\355\231\230\352\262\275\352\265\254\354\266\225.png" "b/Turtle-hwan/chapter01/chapter01_wsl\355\231\230\352\262\275\352\265\254\354\266\225.png"
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diff --git "a/Turtle-hwan/chapter02/chapter02_\354\236\220\353\243\214\355\230\225.png" "b/Turtle-hwan/chapter02/chapter02_\354\236\220\353\243\214\355\230\225.png"
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diff --git a/Turtle-hwan/chapter02/variables b/Turtle-hwan/chapter02/variables
new file mode 100755
index 0000000..4519e1a
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diff --git a/Turtle-hwan/chapter02/variables.c b/Turtle-hwan/chapter02/variables.c
new file mode 100644
index 0000000..828b479
--- /dev/null
+++ b/Turtle-hwan/chapter02/variables.c
@@ -0,0 +1,23 @@
+#include <stdio.h>
+
+void main() {
+    int example = 78;
+    // 서로 다른 자료형의 변수 3개 이상 선언 및 초기화
+
+    char example_char = 'A';            //문자형 변수 1byte / %c로 출력 / 정수로 출력하려면 %hhd
+
+    float example_float = 2.71828182846;    //4byle 단일 정밀도
+
+    double example_double = 2.71828182846;    //8byte 두배정밀도 실수 표현  /   scanf 시는 double 형은 %lf로 받아야 함.
+    
+    
+
+    printf("%d\n", example);
+    // 앞서 선언한 모든 변수를 한 줄에 하나씩 출력
+    printf("문자 출력 : %c   | 정수 출력 : %hhd\n", example_char, example_char);
+
+    printf("float 표현 %%1.16f 출력: %1.16f  | %%f 출력: %f\n", example_float, example_float);
+    //float 형식은 double 보다 부정확
+    printf("double 표현 %%1.16f 출력: %1.16f  | %%f 출력: %f\n", example_double, example_double);    
+    //%f로 출력하면 float이 정확하게 표시할 수 있는 한계만큼 (소수점 아래 6자리 정도) 표현?!
+}
\ No newline at end of file
diff --git "a/Turtle-hwan/chapter03/chapter03_\354\227\260\354\202\260\354\236\220.png" "b/Turtle-hwan/chapter03/chapter03_\354\227\260\354\202\260\354\236\220.png"
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index 0000000..eb4e150
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diff --git a/Turtle-hwan/chapter03/operator b/Turtle-hwan/chapter03/operator
new file mode 100755
index 0000000..7625324
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diff --git a/Turtle-hwan/chapter03/operator.c b/Turtle-hwan/chapter03/operator.c
new file mode 100644
index 0000000..cc4f99f
--- /dev/null
+++ b/Turtle-hwan/chapter03/operator.c
@@ -0,0 +1,88 @@
+#include <stdio.h>
+
+
+void printBin_dec(int dec) {  //십진수를 이진수로 바꾸어 출력
+    int d;
+    if (dec >= 0) {
+        d = dec;
+    }
+    else {
+        d = -dec;
+    }
+    int bin[32] = {0,};
+    int idx = 31;
+    while (d >= 2 && idx != 0) {
+        bin[idx] = d % 2;
+        idx--;
+        d = d / 2;
+    }
+    bin[idx] = 1;
+
+    if (dec < 0) {  //2진법 음수 처리 -> 2의 보수 표현  // 2의 보수 : 1의 보수 + 1
+        for (int i = 31; i >= 0; i--) {  //1의 보수
+            if (bin[i] == 1) {
+                bin[i] = 0;
+            }
+            else {
+                bin[i] = 1;
+            }
+        }
+        if (bin[31] == 1) { // + 1 처리
+            for (int i = 31; i >= 0; i--) {
+                if (bin[i] == 1) {
+                    bin[i] = 0;
+                    continue;
+                }
+                else {
+                    bin[i] = 1;
+                    break; 
+                }
+            }
+        }
+        else {
+            bin[31] = 1;
+        }
+    }
+
+
+    //출력 부분 4자리씩 끊어서
+    printf("%d를 이진수로 바꾼 결과입니다.\n", dec);
+    for (int i = 0; i < 32; i++) {
+        printf("%d", bin[i]);
+        if (i % 4 == 3) {
+            printf(" ");
+        }
+    }
+    printf("\n");
+}
+
+void main() {
+    //int dec = 0b101111;
+    int dec1, dec2;
+
+    printf("연산할 첫 번째 십진수 입력 : ");
+    scanf("%d", &dec1);
+    printf("연산할 두 번째 십진수 입력 : ");
+    scanf("%d", &dec2);
+
+    printBin_dec(dec1);
+    printBin_dec(dec2);
+
+    printf("\n[비트 연산]\n");
+    printf("\n%d & %d = %d\n", dec1, dec2, dec1 & dec2);
+    printBin_dec(dec1 & dec2);
+
+    printf("\n%d | %d = %d\n", dec1, dec2, dec1 | dec2);
+    printBin_dec(dec1 | dec2);
+
+    printf("\n%d ^ %d = %d\n", dec1, dec2, dec1 ^ dec2);
+    printBin_dec(dec1 ^ dec2);
+
+    printf("\n~%d = %d\n", dec1, ~dec1);
+    printBin_dec(~dec1);
+
+    printf("\n%d << 3 = %d\n", dec1, dec1 << 3);
+    printBin_dec(dec1 << 3);
+
+    printf("\nsize of int : %ld byte\n", sizeof(dec1));
+}
diff --git "a/Turtle-hwan/chapter04/chapter04_\354\241\260\352\261\264\353\254\270_A1(printGrade).png" "b/Turtle-hwan/chapter04/chapter04_\354\241\260\352\261\264\353\254\270_A1(printGrade).png"
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index 0000000..922c307
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diff --git a/Turtle-hwan/chapter04/printGrade_switch b/Turtle-hwan/chapter04/printGrade_switch
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index 0000000..67ded0d
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diff --git a/Turtle-hwan/chapter04/printGrade_switch.c b/Turtle-hwan/chapter04/printGrade_switch.c
new file mode 100644
index 0000000..fb4f234
--- /dev/null
+++ b/Turtle-hwan/chapter04/printGrade_switch.c
@@ -0,0 +1,38 @@
+#include <stdio.h>
+
+void main() {
+    int score;
+    printf("점수 입력 : ");
+    scanf("%d", &score);
+
+    switch ((score*2)/10) {
+        case 20:
+        case 19:
+            printf("%d는 A+ 입니다.\n", score);
+            break;
+        case 18:
+            printf("%d는 A 입니다.\n", score);
+            break;
+        case 17:
+            printf("%d는 B+ 입니다.\n", score);
+            break;
+        case 16:
+            printf("%d는 B 입니다.\n", score);
+            break;
+        case 15:
+            printf("%d는 C+ 입니다.\n", score);
+            break;
+        case 14:
+            printf("%d는 C 입니다.\n", score);
+            break;
+        case 13:
+            printf("%d는 D+ 입니다.\n", score);
+            break;
+        case 12:
+            printf("%d는 D 입니다.\n", score);
+            break;
+        default:
+            printf("%d는 F 입니다.\n", score);
+            break;
+    }
+}
\ No newline at end of file