Defining and Initializing Vectors

Introduction

• Discussion continuation on vectors.
• Focus on defining and initializing vectors.

Default Initialization

• Creates an empty vector of a specified type.
• Syntax: vector<Type> vectorName;
• Example: vector<string> svec;
  • Initializes an empty string vector named svec.

Copying Elements from Another Vector

• Creating a vector by copying elements from an existing vector.
• Syntax: vector<Type> newVector(existingVector); or vector<Type> newVector = existingVector;
• Example: vector<int> myvec = {1, 2, 3}; vector<int> newvec(myvec); vector<int> newvec1 = myvec;
  • newvec and newvec1 will both contain elements {1, 2, 3}.
• Type mismatch error if the types do not match: vector<string> svec = myvec; // Error
  • svec (string) ≠ myvec (integer).

List Initializing a Vector

• Creating a vector with zero or more initial values using curly braces {}.
• Syntax: vector<Type> vectorName = {val1, val2, ...}; or vector<Type> vectorName{val1, val2, ...};
• Example: vector<string> colors = {"red", "green", "blue"};
• Common mistake with parentheses (): vector<string> colors("red", "green", "blue"); // Error

Specifying Number of Elements

• Creating a vector with a specified number of elements, optionally with default values.
• Syntax: vector<Type> vectorName(size, value); vector<Type> vectorName(size);
• Examples: vector<int> myvec(5, -2); // Five elements, all -2 vector<string> svec(6, "egg"); // Six elements, all "egg" vector<int> ivec(12); // Twelve elements, default 0

Differences in Bracket Types

• Example variations using parentheses () vs curly braces {}.
• Examples: vector<int> v1(5); // Five elements, default 0 vector<int> v2{5}; // One element, value 5 vector<int> v3(5, 2); // Five elements, all value 2 vector<int> v4{5, 2}; // Two elements, values 5 and 2 vector<string> v5{"cup"}; // One element, "cup" vector<string> v6("cup"); // Error: invalid syntax vector<string> v7{10}; // Ten default-initialized elements; tricky vector<string> v8{10, "cup"};// Ten elements, all "cup"
• Importance of correct bracket usage to avoid errors or different initializations.

Conclusion

• Reviewed various ways to define and initialize vectors.
• Importance of paying attention to bracket types for correct vector initializations.