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# Functions with heap and stack

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### Functions with heap and stack

2. 2. Disclaimer: This presentation is prepared by trainees of baabtra as a part of mentoring program. This is not official document of baabtra –Mentoring Partner Baabtra-Mentoring Partner is the mentoring division of baabte System Technologies Pvt . Ltd
3. 3. • Stores a set of elements in a sequential order • Stack principle: LAST IN FIRST OUT (LIFO) • It means: the last element inserted, is the first one to be removed Which is the first element to pick up? The Stack Example
4. 4. • When a function declares a new variable, it is pushed onto the stack. • And when it exits, all of the variables pushed by that function, are freed (means deleted). • So that region of memory becomes available for other stack variables. Stack in functions
5. 5. public int factorial (int x) { if (x > 1) { //recursive case: return factorial(x-1) * x; } else /*base case*/ return 1; } Factorial(3){ If(3>1){ return factorial (2)*3 Factorial(2){ If(2>1){ return factorial (1)*2 Factorial(1){ If(1>1){ return 1; Example of Stack in recursive function 1 2 Final output: 6
6. 6. Example for Stack #include <stdio.h> double multiplyByTwo (double input) { double twice = input * 2.0; return twice; } int main (int argc, char *argv[]) { int age = 30; double salary = 12345.67; double myList[3] = {1.2, 2.3, 3.4}; printf("double your salary is %.3fn", multiplyByTwo(salary)); return 0; }
7. 7. The Heap • The heap is an area of memory reserved for dynamic memory allocation. • Dynamic memory can be allotted by calling the malloc( ) function in C. • When this memory is no longer needed it can be freed up by calling free( ) . • Once the memory is freed it can reused by future allocations. • The location and size of the heap are set at compile time.
8. 8. Example for Heap #include <stdio.h> #include <stdlib.h> double *multiplyByTwo (double *input) { double *twice = malloc(sizeof(double)); *twice = *input * 2.0; return twice; } int main (int argc, char *argv[]) { int *age = malloc(sizeof(int)); *age = 30; double *salary = malloc(sizeof(double)); *salary = 12345.67; double *myList = malloc(3 * sizeof(double)); myList[0] = 1.2; myList[1] = 2.3; myList[2] = 3.4; double *twiceSalary = multiplyByTwo(salary); printf("double your salary is %.3fn", *twiceSalary); free(age); free(salary); free(myList); free(twiceSalary); return 0; }
9. 9. Both programs will show output as : double your salary is 24691.340
10. 10. Stack • very fast access • don't have to explicitly de-allocate variables • space is managed efficiently by CPU, memory will not become fragmented • local variables only • limit on stack size (OS-dependent) • variables cannot be resized Stack vs Heap Pros and Cons
11. 11. Heap • variables can be accessed globally • no limit on memory size • (relatively) slower access • no guaranteed efficient use of space, memory may become fragmented over time as blocks of memory are allocated, then freed • you must manage memory (you're in charge of allocating and freeing variables) • variables can be resized using realloc() Stack vs Heap Pros and Cons
12. 12. Doubts…?
13. 13. thank you
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