diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..2490a4d
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,2 @@
+*.o
+/calc
diff --git a/README.md b/README.md
new file mode 100644
index 0000000..68b2d37
--- /dev/null
+++ b/README.md
@@ -0,0 +1,16 @@
+# Simple Calculator
+
+This is a buggy application that will be used for Lab5 of 'Introduction to Open Source Software Development.'
+
+  - Fork the project.
+  - Create a topic branch from master. 
+  - The branch name must be your student id. (e.g. 201624000)
+  - Make some commits to improve the project.
+    - Fix the well-knwon bugs.
+    - Remove object and binary files.
+    - Add .gitignore file
+  - Push this branch to your GitHub project.
+  - Open a Pull Request on GitHub.
+  - The Pull Request must be submitted to master branch of Classroom-IOSSD/SimpleCalculator!
+  - Capture the Pull Request and upload it to PLMS.
+
diff --git a/calc.c b/calc.c
index 85f1466..b03877f 100644
--- a/calc.c
+++ b/calc.c
@@ -5,28 +5,29 @@ int main(){
 	FILE *fp = NULL;
 	int operand1, operand2;
 	char operator = ' ';
-	int result, line = 0;
+	float result, line = 0;
 
 	fp = fopen("read.txt","r");
 	if(fp!=NULL){
-		fscanf(fp, "%d", &line);
+		fscanf(fp, "%f", &line);
 	
 		for(int i=0; i<line; i++) {
 			fscanf(fp, "%d %c %d",&operand1, &operator, &operand2);
 			switch(operator) {
 				case '+':
-				result = add(operand1, operator);
+				result = add(operand1, operand2);
 				break;
 				case '-':
-				result = minus(operand1, operator);
+				result = minus(operand1, operand2);
 				break;
 				case '*':
-				result = mul(operand1, operator);
+				result = mul(operand1, operand2);
+				break;
 				case '/':
-				result = div(operand1, operator);
+				result = div(operand1, operand2);
 				break;
 			}		
-			printf("%d %c %d = %d\n",
+			printf("%d %c %d = %f\n",
 				 operand1, operator, operand2, result);
 		}
 	}
diff --git a/operators.c b/operators.c
index d51cb3e..33f4e64 100644
--- a/operators.c
+++ b/operators.c
@@ -1,16 +1,16 @@
 #include "operators.h"
 
-int add(int op1, int op2) {
+double add(int op1, int op2) {
 	return op1+op2;
 }
-int minus(int op1, int op2) {
+double minus(int op1, int op2) {
 	return op1-op2;
 }
-int mul(int op1, int op2) {
+double mul(int op1, int op2) {
 	return op1*op2;
 }
 
-int div(int op1, int op2) {
-	return op1%op2;
+double div(float op1, float op2) {
+	return op1/op2;
 }
 
diff --git a/operators.h b/operators.h
index bd08f7d..62e3875 100644
--- a/operators.h
+++ b/operators.h
@@ -1,4 +1,4 @@
-int add(int op1, int op2);
-int mul(int op1, int op2);
-int div(int op1, int op2);
-int minus(int op1, int op2);
+double add(int op1, int op2);
+double mul(int op1, int op2);
+double div(float op1, float op2);
+double minus(int op1, int op2);
diff --git a/read.txt b/read.txt
index 3e2bf01..8c26ad2 100644
--- a/read.txt
+++ b/read.txt
@@ -1,4 +1,4 @@
-5
+4
 123 + 456
 234 * 234
 143 - 111