For[i = 0; v = 0, i < 101, i++, v = v + i^2]

v

Sum[i^2, {i, 0, 100}]

For[i = 0; v = 0, i < 101, i++, 
        v = v + i^2];
Print[v]

k0 = 5;
For[k = 1; v = 0, 
        k < k0 + 1, k++, 
For[j = 1, 
          j < k + 1, j++, 
          v = v + a[j, k]]
];
Print[v]

For[i = 0, i < 31, i++, a = 1 + i/10; 
      Plot[Sin[a x], {x, 0, 2  Pi}]]

100!

For[n = 1, n < 11, n++, 
      Plot[Sum[x^j/j!, {j, 0, n}], {x, -7, 7}, 
        PlotRange -> {-5, 30}]]

For[n = 0; a = 1; b = 1; Print[a]; Print[b], n < 101, n++, 
      c = a + b; a = b; b = c; Print[b]]