Stacks are a type of container adaptors with LIFO(Last In First Out) type of working, where a new element is added at one end and (top) an element is removed from that end only.
stack::top()
top() function is used to reference the top(or the newest) element of the stack.
Syntax :
stackname.front() Parameters : No value is needed to pass as the parameter. Returns : Direct reference to the top element of the stack container.
Examples:
Input : stackname.push(5);
stackname.push(1);
stackname.top();
Output : 1
Input : stackname.push(5);
stackname.push(1);
stackname.push(2);
stackname.top();
Output : 2
Errors and Exceptions
1. If the stack container is empty, it causes undefined behaviour
2. It has a no exception throw guarantee if the stack is not empty
// CPP program to illustrate // Implementation of top() function #include <iostream> #include <stack> using namespace std; int main() { stack<int> mystack; mystack.push(5); mystack.push(1); mystack.push(2); // Stack top cout << mystack.top(); return 0; } |
Output:
2
Application :
Given a stack of integers, find the sum of the all the integers.
Input : 1, 8, 3, 6, 2 Output: 20
Algorithm
1. Check if the stack is empty, if not add the top element to a variable initialised as 0, and pop the top element.
2. Repeat this step until the stack is empty.
3. Print the final value of the variable.
// CPP program to illustrate // Application of top() function #include <iostream> #include <stack> using namespace std; int main() { int sum = 0; stack<int> mystack; mystack.push(1); mystack.push(8); mystack.push(3); mystack.push(6); mystack.push(2); // Stack becomes 1, 8, 3, 6, 2 while (!mystack.empty()) { sum = sum + mystack.top(); mystack.pop(); } cout << sum; return 0; } |
Output:
20
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