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Definition and relation of formal parameter and argument
Relation between formal parameter and actual parameter:
Shape participating arguments of one-dimensional array as function
Shape participating arguments of one-dimensional array as function
Array as function parameter (in the form of pointer)
main function parameter problem
Definition and relation of formal parameter and argument
Formal parameters:
Parameters specified when defining a function. The parameter appearing in the function definition can be regarded as a placeholder. It has no data and can only wait until the function is called to receive the data passed in, so it is called formal parameter for short.
The memory of formal parameter variables will be allocated only when the function is called, and the memory will be released immediately after the call, so the formal parameter variables are only valid inside the function and cannot be used outside the function.
Actual parameters:
The specified parameters when calling the function. The parameters given when the function is called contain real data and will be used by the internal code of the function, so they are called actual parameters for short.
Arguments can be constants, variables, expressions, functions, etc. no matter what type of data the arguments are, they must have definite values when calling functions, so that these values can be transmitted to formal parameters. Therefore, assignment, input and other methods should be used in advance to make the arguments obtain definite values.
Relation between formal parameter and actual parameter:
The function of formal and actual parameters is to pass data. When a function call occurs, the value of the actual parameter will be passed to the formal parameter.
Array as function parameter
Shape participating arguments of one-dimensional array as function
int a[10]; void function(int a[],int n) //Formal parameters function(a,10) //Actual parameters
Shape participating arguments of one-dimensional array as function
int a[5][10]; void function(int a[][10],int n) //Formal parameters function(a,5) //Actual parameters
Array as function parameter (in the form of pointer)
Some students will have questions. Didn't it just say that arrays are function parameters? Why did it come in the form of pointers. Don't worry, we all know that array is also a pointer (that is, address), so array can also be expressed in the form of pointer. I put this part here, just as the buffer for array to do function parameters and pointer to do function parameters
We will directly use an example to compare the difference between the two forms of array as a function parameter, in order to obtain the maximum value in a one-dimensional array
/*
find_max:Find the maximum value of one-dimensional array by using array as parameters
@a[]:One dimensional array that needs to be maximized
@n: Number of elements of one-dimensional array
Return value
max: Maximum value of one-dimensional array
*/
int find_max(int a[],int n)
{
int i;
int max = a[0];
for(i = 0; i < n; i++)
{
if(a[i] > max)
{
max = a[i];
}
}
return max;
}/*
find_max:Array takes the form of pointer as a parameter to find the maximum value of one-dimensional array
@a[]:One dimensional array that needs to be maximized
@n: Number of elements of one-dimensional array
Return value
max: Maximum value of one-dimensional array
*/
int find_max(int *b,int n)
{
int i;
int max = *b; //*b = *&b[0]= b[0]
for(i = 0; i < n; i++)
{
if(*(b+i) > max)
{
max = *(b+i);
}
}
return max;
}In order to make it more difficult for you to better understand, let's use arrays as parameters in the form of pointers to input and output a two-dimensional array
void _3()
{
int a[3][3];
for(int i = 0;i<3;i++)
{
for(int j = 0;j < 3;j++)
{
scanf("%d",(*(a+i)+j)); //The input of two-dimensional array is equivalent to scanf("%d",a[i][j]);
}
}
for(int i = 0;i<3;i++)
{
for(int j = 0;j < 3;j++)
{
printf("%d ",*(*(a+i)+j)); //The output of two-dimensional array is equivalent to printf ("%d", a[i][j]);
}
printf("\n");
}
printf("\n");
}Pointer as function parameter
/*
_17:Use the pointer as a parameter to exchange two values
*/
void _17(int *p,int *q)
{
int t;
t = *p;
*p = *q;
*q = t;
}
int main()
{
int a = 0,b = 1;
_17(&a,&b);
printf("a = %d, b = %d\n",a,b);
}void func(int *p)
{
*p = 250;
}
int main()
{
int a;
func(&a);//p = &a;
//typeof(p): int *
//typeof(&a): typeof(a)* int *
printf("%d\n",a);
}main function parameter problem
Talking about the main function, we can certainly quickly type the sentence "int main() {}", but the main function actually has three optional parameters, as follows
int main(int argc, char *argv[], char *envp[]);
argc: is an int type, which represents the number of parameters on the command line
argv: char*[], is an array of string pointers.
argv[0]: the address of the first parameter string of the program is saved
argv[1]: the address of the second parameter string of the program is saved
....
argv[argc] is NULL, indicating the end of the parameter.
char* envp[], which is also a string array, is mainly used to save the variable string in the user environment and ends with NULL.
According to the provisions of C language, the value of argv[0] is the program name that starts the program.
eq: ./a.out ./hello
So the value of agrc is at least one. If the value of agrc is 1, there is no command line parameter after the program name.
Let's try to print out the command line parameters entered on the terminal. Also test the third parameter
int main(int argc,char *argv[]) //Print commands entered by the terminal
{
int i = 0;
while(argv[i++])
{
printf("%s ",argv[i]);
}
printf("\n");
i = 0;
while(envp[i++])
{
printf("%s\n", envp[i]);
}
return 0;
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