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POissue in making Queue data structure as array implementation
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copied!<p>this code to make simple queue data structure as array implementation</p> <pre><code>#include <stdio.h> #define Q_MAX_SIZE 255 #include <stdbool.h> struct queue { int* pointer; int* currentValue; int max, count, theQueue[Q_MAX_SIZE]; }; void initQueue(struct queue*); bool pushQueue(struct queue*, int); int* popQueue(struct queue*); int main(void) { int i, j, num = 0; struct queue obj[5]; for(i=0; i<5; i++) { initQueue(&obj[i]); for(j = 0; j<3; j++) { num++; pushQueue(&obj[i], num); } num = 0; } for(i=0; i<5; i++) { printf("Queue[%d]:\n", i); int* inputobj; inputobj = popQueue(&obj[i]); while(inputobj != NULL) { printf("Queue[No.%d] = %d\n", i, *inputobj); inputobj = popQueue(&obj[i]); } putchar('\n'); } puts("done..!"); return 0; } //@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ void initQueue(struct queue *Q) { Q->pointer = Q->theQueue; Q->max = Q_MAX_SIZE; Q->count = 0; } bool pushQueue(struct queue *Q, int input) { if(Q->count < Q->max) { *Q->pointer = input; Q->pointer++; Q->count++; return 1; } else return 0; } //@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ int* popQueue(struct queue *Q) { int i; if(Q->count > 0) { Q->currentValue = Q->theQueue; Q->pointer--; Q->count--; for(i=0; i < Q->count; i++) { int* currentPtr = Q->theQueue + i; int* nextPtr = currentPtr + 1; *currentPtr = *nextPtr; } return Q->currentValue; } else NULL; } </code></pre> <p>there is a problem with the code in the function <code>popQueue()</code> in this line: </p> <p><code>Q->currentValue = Q->theQueue;</code></p> <p>it is work put the output is not correct</p> <pre><code>output: Queue[0]: Queue[No.0] = 2 Queue[No.0] = 3 Queue[No.0] = 3 Queue[1]: Queue[No.1] = 2 Queue[No.1] = 3 Queue[No.1] = 3 Queue[2]: Queue[No.2] = 2 Queue[No.2] = 3 Queue[No.2] = 3 Queue[3]: Queue[No.3] = 2 Queue[No.3] = 3 Queue[No.3] = 3 Queue[4]: Queue[No.4] = 2 Queue[No.4] = 3 Queue[No.4] = 3 done..! </code></pre> <p>but after i change the pointer (<code>currentValue</code>) in the <code>queue</code> struct to make it of type integer and edit some lines in the function <code>popQueue()</code> every thing work fine.</p> <p><strong>--here is the function after editing:</strong></p> <pre><code>int* popQueue(struct queue *Q) { int i; if(Q->count > 0) { Q->currentValue = Q->theQueue[0]; Q->pointer--; Q->count--; for(i=0; i < Q->count; i++) { int* currentPtr = Q->theQueue + i; int* nextPtr = currentPtr + 1; *currentPtr = *nextPtr; } return &Q->currentValue; } </code></pre> <p>-- and this is the correct output:</p> <pre><code>Queue[0]: Queue[No.0] = 1 Queue[No.0] = 2 Queue[No.0] = 3 Queue[1]: Queue[No.1] = 1 Queue[No.1] = 2 Queue[No.1] = 3 Queue[2]: Queue[No.2] = 1 Queue[No.2] = 2 Queue[No.2] = 3 Queue[3]: Queue[No.3] = 1 Queue[No.3] = 2 Queue[No.3] = 3 Queue[4]: Queue[No.4] = 1 Queue[No.4] = 2 Queue[No.4] = 3 </code></pre> <h2>The Question is: what makes the first code provide wrong output?</h2>

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