How to properly align triangular number patterns - c

Question

In C, I need to print the number pattern in the below manner in right alignment, ie: when the double digit comes the upper single digit should adjust itself to right and so on.
int main() {
long int k = 1;
int i, j, n;
scanf("%d", &n);
for (i = 1; i <= n; i++) {
for (j = 1; j <= i; j++) {
printf("%ld ", k);
k++;
}
printf("\n");
}
return 0;
}
required output:
1
2 3
4 5 6
7 8 9 10
11 12 13 14 15
16 17 18 19 20 21
22 23 24 25 26 27 28
29 30 31 32 33 34 35 36
37 38 39 40 41 42 43 44 45
46 47 48 49 50 51 52 53 54 55 `
output I get:
1
2 3
4 5 6
7 8 9 10
11 12 13 14 15
16 17 18 19 20 21
22 23 24 25 26 27 28
29 30 31 32 33 34 35 36
37 38 39 40 41 42 43 44 45
46 47 48 49 50 51 52 53 54 55
output required:
1
2 3
4 5 6
7 8 9 10
11 12 13 14 15
16 17 18 19 20 21
22 23 24 25 26 27 28
29 30 31 32 33 34 35 36
37 38 39 40 41 42 43 44 45
46 47 48 49 50 51 52 53 54 55
56 57 58 59 60 61 62 63 64 65 66
67 68 69 70 71 72 73 74 75 76 77 78
79 80 81 82 83 84 85 86 87 88 89 90 91
92 93 94 95 96 97 98 99 100 101 102 103 104 105
106 107 108 109 110 111 112 113 114 115 116 117 118 119 120
121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136
137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153
154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171
172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190
191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210
output I get:
1
2 3
4 5 6
7 8 9 10
11 12 13 14 15
16 17 18 19 20 21
22 23 24 25 26 27 28
29 30 31 32 33 34 35 36
37 38 39 40 41 42 43 44 45
46 47 48 49 50 51 52 53 54 55
56 57 58 59 60 61 62 63 64 65 66
67 68 69 70 71 72 73 74 75 76 77 78
79 80 81 82 83 84 85 86 87 88 89 90 91
92 93 94 95 96 97 98 99 100 101 102 103 104 105
106 107 108 109 110 111 112 113 114 115 116 117 118 119 120
121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136
137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153
154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171
172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190
191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210

Answer 1

You should calculate the length of the last outputted number and use the value as the field width in a printf call..
Here you are.
#include <stdio.h>
int main(void)
{
while ( 1 )
{
printf( "Enter a non-negative number (0 - exit): " );
unsigned int n;
if ( scanf( "%u", &n ) != 1 || n == 0 ) break;
unsigned int upper = n * ( n + 1 ) / 2;
int size = 0;
do { ++size; } while ( upper /= 10 );
putchar( '\n' );
for ( unsigned int i = 0, value = 0; i < n; i++ )
{
do
{
printf( "%*u ", size, ++value );
} while ( value != ( i + 1 ) * ( i + 2 ) / 2 );
putchar( '\n' );
}
putchar( '\n' );
}
return 0;
}
The program output is
Enter a non-negative number (0 - exit): 10
1
2 3
4 5 6
7 8 9 10
11 12 13 14 15
16 17 18 19 20 21
22 23 24 25 26 27 28
29 30 31 32 33 34 35 36
37 38 39 40 41 42 43 44 45
46 47 48 49 50 51 52 53 54 55
Enter a non-negative number (0 - exit): 20
1
2 3
4 5 6
7 8 9 10
11 12 13 14 15
16 17 18 19 20 21
22 23 24 25 26 27 28
29 30 31 32 33 34 35 36
37 38 39 40 41 42 43 44 45
46 47 48 49 50 51 52 53 54 55
56 57 58 59 60 61 62 63 64 65 66
67 68 69 70 71 72 73 74 75 76 77 78
79 80 81 82 83 84 85 86 87 88 89 90 91
92 93 94 95 96 97 98 99 100 101 102 103 104 105
106 107 108 109 110 111 112 113 114 115 116 117 118 119 120
121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136
137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153
154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171
172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190
191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210
Enter a non-negative number (0 - exit): 0

Answer 2

I will not help you write a code because zero effort is shown, but I can give hints via a pseudo code.
cin >> n; //desired number of rows
for (int i = 0; i < n; i++){
//generate triangle numbers
}//store the first n triangle numbers, given by n(n-1)/2
for (int i = 0; i < n; i++){
cout << i;
if (i==any triangle number){
cout << "\n"; //note that an endline is printed only at triangle numbers
}
}

Answer 3

Here is a simple solution that handles end of lines correctly too:
#include <stdio.h>
int main(void) {
int i, j, k, n, len;
if (scanf("%d", &n) == 1 && n > 0) {
/* compute the width of the last number */
//len = snprintf(NULL, 0, "%d", n * (n + 1) / 2);
//char buf[48]; /* large enough for 128-bit integers */
//len = sprintf(buf, "%d", n * (n + 1) / 2);
for (len = 1, k = n * (n + 1) / 2; k > 9; k /= 10)
len++;
for (i = k = 1; i <= n; i++) {
for (j = 1; j < i; j++) {
printf("%*d ", len, k++);
}
/* print the last number on the line without a trailing space */
printf("%*d\n", len, k++);
}
}
return 0;
}