Why is the output junk value-CodePudding

In the below code, When I did the same logic without using functions it gave correct answer. But with using functions its giving some junk value. The question was to print the sum of diagonal matrix in array using c using functions.

#include<stdio.h>
int read(int a[][100],int,int);
int displayres(int a[][100],int,int);
int main()
{
    int m,n,a[100][100];
    printf("Enter the number of rows: ");
    scanf("%d",&m);
    printf("Enter the number of columns: ");
    scanf("%d",&n);
    if(m==n)
        read(a,m,n);
    displayres(a,m,n);
}


int read(int a[][100],int m,int n)
{
    int i,j;
    if(m==n)
    printf("Enter the elements:\n");
    for(i=0;i<m;i  )
    {    
        for(j=0;j<n;j  )
        {
            scanf("%d",&a[i][j]);
        }
    }
    
}



int displayres(int a[][100],int m,int n)
{
    int i,j,abc;
    
        for(i=0,j=0;i<m,j<n;i  ,j  )
        {
            abc = abc   a[i][j];
        }
    printf("%d\n",abc);  
        
}

CodePudding user response：

As the diagonal is processed for quadratic matrices then these declarations of the functions

int read(int a[][100],int,int);
int displayres(int a[][100],int,int);

do not make a great sense. One parameter is redundant. The functions can be declared like

void read(int a[][100], size_t );
int displayres(int a[][100], size_t );

correspondingly instead of these two prompts

printf("Enter the number of rows: ");
scanf("%d",&m);
printf("Enter the number of columns: ");
scanf("%d",&n);

you should use only one prompt and also you need to check that the entered number (for example n) is not greater than 100.

As the function read returns nothing its return type should be void.

Its definition can look like

void read(int a[][100], size_t n )
{
    printf("Enter the elements:\n");
    for ( size_t i = 0; i < n; i   )
    {    
        for ( size_t j = 0; j < n; j   )
        {
            scanf("%d",&a[i][j]);
        }
    }
}

Within the function displayres you forgot to initialize the variable abc. And the function should not output anything. It should return the calculated value. The function can look the following way

int displayres(int a[][100], size_t n )
{
    int abc = 0;
    
    for ( size_t i = 0; i < n; i   )
    {
        abc  = a[i][i];
    }

    return abc;        
}

And in main you can write

printf( "The sum is %d\n", displayres( a, n ) );

If you want to calculate the sum for a matrix of any sizes then the function displayres can look the following way

int displayres( int a[][100], size_t m, size_t n )
{
    int abc = 0;
    
    for ( size_t; i < m && i < n; i   )
    {
        abc  = a[i][i];
    }

    return abc;        
}

As for your for loop then you are using the comma operator in the condition

    for(i=0,j=0;i<m,j<n;i  ,j  )

It is the same as to write

    for( i=0, j=0; j < n; i  ,j   )

because the value of the first operand of the comma operator is discarded.