C语言程序设计课件PPT（英文）C program language 之6 Points and Array.pptVIP

Points and Array static int a[3][3]={ 1, 2,3, 4,5,6,7,8,9 }; int *pa[3]={ a[0], a[1], a[2] }; 1 2 3 4 5 6 7 8 9 a[0] a[1] a[2] *pa[0] *pa[1] *pa[2] 6 use pointer array access the elements in 2D array Use address to initialize pointer array We think the each row as an 1D array , and the name is a[0],a[1],a[2]. So a[0],a[1],a[2] are addresses too. For ith row , pa[i] point to the first element of that array a[i] Pointer Arrays Pointers and Addresses main( ) { int a,b,c; int *p ; /*declare a pointer*/ a=100; b=200; p=c; /*assign address of c to p*/ *p=a+b; /*assign a+b to the c */ printf(“%d+%d=%d\n”,a,b,*p); printf(“%x,%x,%x,%x,%x\n”, a,b,c,p,p); } main( ) { float a,b,c; float *p; a=100.0,b=200.0; p=c; *p=a+b; printf(“%f+%f = %f \n”, a, b, *p); printf(“%x,%x,%x,%x,%x\n”, a, b, c, p,p); } 100 200 300 a b c p Pointers and Addresses Some examples: *ip = *ip + 10; y = *ip + 1 *ip += 1 ++*ip (*ip)++ Since pointers are variables, if iq is another pointer to int, iq = ip copies the contents of ip into iq, thus making iq point to whatever ip pointed to. int *ip; ip = x; int x = 1, y = 2 ; *ip , x : 11 y: 12 *ip: 12 *ip: 13 *ip: 14 Pointers and Function Arguments main( ) { int a , b; printf(“Enter two numbers:\n”); scanf(“%d,%d”,a,b); printf(“ 1: %d,%d\n”,a,b); swap( a, b ); printf(“3:%d,%d\n”,a,b); } swap(int x,int y) { int c; c=x ; x=y ; y=c ; printf(“2: %d,%d\n”,x, y); } swap( a, b ); Input:3，5 output1：3，5 output2：5，3 3 ，5 output3：3，5 Formal arguments x , y are local variables , their value can only be used within the function. Pointers and Function Arguments swap( int *p1, int *p2) { int pk; pk=*p1; *P1=*P2; *p2=pk; printf(“2: %d,%d\n”, *p1, *p2); } main( ) { int a , b; int