[英]Implement a stack by using a pointer to pointer
我正在實現一個使用雙指針進行練習的小程序,這是主程序:
#include <stdio.h>
#include "serial.h"
#include "stack.h"
int main(void) {
serial_init();
/* Array to hold stack entries */
int stack[10]={0};
/* Stack pointer */
int *stack_p = stack;
/* Code to call the functions */
push(&stack_p, 1);
push(&stack_p, 2);
push(&stack_p, 3);
push(&stack_p, 4);
printf("popped value: %d\r\n", pop(&stack_p));
printf("popped value: %d\r\n", pop(&stack_p));
printf("popped value: %d\r\n", pop(&stack_p));
printf("popped value: %d\r\n", pop(&stack_p));
}
void push(int **sp, int value) {
/* Implement it */
}
int pop(int **sp) {
/* Implement it */
}
我已經實現了推功能,看來還可以。 但是,彈出窗口僅返回最后一個元素,然后返回10
void push(int **sp, int value) {
/* implemented it*/
int *pt;
pt=&value; // Store the value to the pointer
printf("Push value is is %d\r\n", *pt);
sp = &pt; // associate the pointer to the pointer of pointer
++(*pt);
}
int pop(int **sp) {
/* implemented it */
int value;
int *pt;
pt=&value;
sp = &pt;
*pt--;
return value;
}
您的push和pop函數過於復雜且完全錯誤:
你要這個:
void push(int **sp, int value) {
**sp = value; // put value onto top of the stack
(*sp)++; // increment stack pointer
}
int pop(int **sp) {
(*sp)--; // decrement stack pointer
return **sp; // return value which is on nthe op of the stack
}
您輸入的錯誤代碼帶有注釋說明:
void push(int **sp, int value) {
int *pt;
pt=&value; // here you put the pointer to the local variable value
// into pt, but local variables disappear as soon
// as the function has finished
// the printf is the only thing one more or less correct
// but you could just print directly 'value' like this:
// printf("Pushed value is %d\r\n", value);
//
printf("Push value is is %d\r\n", *pt);
sp = &pt; // this only assigns the pointer to the local variable pt to
// the local variable sp
++(*pt); // here you increment actually the local variable
// value which is pointless
}
順便說一句:盡管在調試過程中可能會有所幫助,但不必將整個堆棧初始化為零。 因此,您可以像這樣編寫堆棧的聲明:
int stack[10]; // no initialisation necessary
為您練習:
說明不需要將堆棧的所有元素初始化為零的確切原因。
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