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Pointers

Pointers. Value, Address, and Pointer. Values and Addresses. int x, y, z;. x = 5;. x. y = x + 5;. y. z = y + 5;. z. values of x, y, and z x is 5 y is 10 z is 15. addresses of x, y, and z &x is 70000 &y is 70004 &z is 70008. Example 1. #include < stdio.h >

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Pointers

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  1. Pointers Value, Address, and Pointer

  2. Values and Addresses int x, y, z; x = 5; x y = x + 5; y z = y + 5; z • values of x, y, and z • x is 5 • y is 10 • z is 15 • addresses of x, y, and z • &x is 70000 • &y is 70004 • &z is 70008

  3. Example 1 • #include <stdio.h> • int main(void) { • int x, y, z; • x = 5; • y = 10; • z = x + y; • printf("The value of x is: %3d\n", x); • printf("The value of y is: %3d\n", y); • printf("The value of z is: %3d\n", z); • printf("\n"); • printf("The address of x is: %d\n", &x); • printf("The address of y is: %d\n", &y); • printf("The address of z is: %d\n", &z); • return(0); • }

  4. Pointers int *p, *q; p = &x; x q = &y; y z = *p + *q + 3; z values of p and q • p is 70000 • q is 70004 p q addresses of p and q • &p is 70012 • &qis 70016 values pointed by p and q • *p is 5 • *q is 10

  5. Example 2 • printf("The address of x is: %d\n", &x); • printf("The address of y is: %d\n", &y); • printf("\n"); • printf("The value of p is: %3d\n", p); • printf("The value of q is: %3d\n", q); • printf("\n"); • printf("The value of x is: %3d\n", x); • printf("The value of y is: %3d\n", y); • printf("\n"); • printf("The value of x is: %3d\n", *p); • printf("The value of y is: %3d\n", *q); • printf("\n"); • printf("The value of z is: %3d\n", z); • return(0); • } • #include <stdio.h> • int main(void) { • int x, y, z; • int *p, *q; • x = 5; • y = 10; • p = &x; • q = &y; • z = *p + *q + 3;

  6. Example 3 int x, y; int *px, *py; x = 3; y = 5; px = &x; py = &y printf(“%d”, *px); *px = 1; printf(“%d”, *px); *py = 7; py = px; printf(“%d”, *px);

  7. Example 4 – Scope of variable • #include <stdio.h> • void DoIt(int x); • int main(void) { • int x; • x = 3; • printf("Before calling function: %d\n", x); • DoIt(x); • printf("After calling function: %d\n", x); • return(0); • } • void DoIt(int x) { • x = 44; • printf("Inside the function: %d\n", x); • }

  8. Example 5 – Scope of variable • #include <stdio.h> • void DoIt(int *x); • int main(void) { • int x; • x = 3; • printf("Before calling function: %d\n", x); • DoIt(&x); • printf("After calling function: %d\n", x); • return(0); • } • void DoIt(int *x) { • *x = 44; • printf("Inside the function: %d\n", *x); • }

  9. Sort • Problem: Sort three numbers in ascending order • Analysis: Put minimum in 1st, next minimum in 2nd • Design: • Compare 1st &2nd, put smaller in 1st, • Compare 1st & 3rd, put smaller in 1st, • Compare 2nd & 3rd, put smaller in 2nd • Use function for sort called MySort takes three pointers and sorts the contents. Does not return a value • Use a function for exchanging two values called xChange which takes two pointers and exchanges the contents.

  10. Sort • Code: • Test: • Try 1 2 3  output 1 2 3 • Try 3 2 1  output 1 2 3 • Try 5 8 2  output 2 5 8 • Try 8 2 5  output 2 5 8 • Maintain: Correct errors, make improvements, add new functionality

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