diff --git a/education/software development/ECE1400/Chapter 13 Exercises.md b/education/software development/ECE1400/Chapter 13 Exercises.md
index 7590c81..a953771 100644
--- a/education/software development/ECE1400/Chapter 13 Exercises.md	
+++ b/education/software development/ECE1400/Chapter 13 Exercises.md	
@@ -38,4 +38,23 @@ scanf("%d%s%d", &i, s, &j);
 
 ---
 
-> **7.** Suppose that `str`
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+> **7.** Suppose that `str` is an array of three characters. Which one of the following statements is not equivalent to the other three?
+```c
+// A
+*str = 0;
+// B
+str[0] = '\0';
+// C
+strcpy(str, "");
+// D
+strcat(str, "");
+```
+(d) is different because it effectively does nothing (concatenates `"abc"` with an empty string). The rest of them make `str` effectively empty by setting the first character to a null byte.
+
+---
+
+> **9.** What will be the value of the string `s1` after the following statements have been executed?
+```c
+strcpy(str, "tire-bouchon");
+strcpy(&str[4], "d-or-wi")
+```
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