如何在C中终止程序？

Question

so i'm done with my code and it gives the required output, but it doesn't terminate! how can i fix it? i tried return but didn't find the right place to keep it so i'm done with my code and it gives the required output, but it doesn't terminate! how can i fix it? i tried return but didn't find the right place to keep it

#include<stdio.h>

void get_input();   
void is_valid(int num);  
void print_pattern(int num);  

void main ()
{
    get_input();    
}

void get_input()
{
    int a;
    printf("Enter an odd number less than or equal to 9 and greater than 0 > "); 
    scanf("%d",&a);
    is_valid(a);
}

void is_valid(int num)
{
    if(num > 9)
        printf("You have entered a number greater than 9. Please try again.\n\n"); 
    else if (num < 1)
        printf("You have entered a number less than 1. Please try again.\n\n"); 
    else if (num % 2 == 0)
        printf("You have entered an even number. Please try again\n\n"); 
    else if (num >= 1 && num <= 9 && num%2!=0)    
        print_pattern(num);
    get_input();              
}

void print_pattern(int num)
{
    int j,k,l;
    for ( j = 0; j<num/2 ; j++ ){
        for ( k = 0; k<num/2 - j; k++){
            printf("  ");
        }
        for( l=0; l < (2*j + 1); l++){
            printf("%2d",l+1);
        }
        printf("\n");    
    }    

    for( l=0; l <num; l++) // to print middle
    {
        printf("%2d",l+1);
    }
    printf("\n");

    // to print bottom
    for ( j = 0; j<num/2 ; j++){
        for ( k = 0; k<j+1 ; k++){
            printf("  ");
        }
        for ( l=1; l< num - (2*j + 1); l++){
            printf("%2d",l);
        }
        printf("\n");
    }        
}

Answer 1

It's in endless loop

main calls get_input which calls is_valid which calls get_input making a indirect recursion there.

If you want to terminate, enter some if condition for num like if (num < 0) return

Answer 2

When you use if-else statement, you should use {} to create a block, unless the block is single lined.

For example, when you use

if(num > 9)
printf("You have entered a number greater than 9. Please try again.\n\n"); 
else if (num < 1)
printf("You have entered a number less than 1. Please try again.\n\n"); 
else if (num % 2 == 0)
printf("You have entered an even number. Please try again\n\n"); 
else if (num >= 1 && num <= 9 && num%2!=0)
print_pattern(num);
get_input();          

it will be read as

if(num > 9)
{
    printf("You have entered a number greater than 9. Please try again.\n\n"); 
}
else if (num < 1)
{
    printf("You have entered a number less than 1. Please try again.\n\n"); 
}
else if (num % 2 == 0)
{
    printf("You have entered an even number. Please try again\n\n"); 
}
else if (num >= 1 && num <= 9 && num%2!=0)
{
    print_pattern(num);
}
get_input(); 

This will result in calling get_input() each time you call is_valid(), ending in an endless loop. to prevent the loop, insert the call to get_input() only when needed.

Furthermore, make sure that your blocks (the parts between each { }) are well defined, and you are not closing them prematurely or opening blocks without closing them. This can also result in looping, especially if done wrong where you have loops.

Also, regarding the if-else statements, the last else-if is redundant. If num is neither greater than 9, nor even, nor smaller than 1, then it must be a legal input, and there is no need to add the if statement there.

Answer 3

main() should end with return 0 if your program succeeded. Here's a short explanation of some status codes you can return: https://stackoverflow.com/a/22604382/1137699